Respiratory uncoupling lowers blood pressure through a leptin-dependent mechanism in genetically obese mice

Hypothalamic free fatty acid receptor-1 regulates whole-body energy balance

OBJECTIVE

Free fatty acid receptor-1 (FFAR1) is a medium- and long-chain fatty acid sensing G protein-coupled receptor that is highly expressed in the hypothalamus. Here, we investigated the central role of FFAR1 on energy balance.

METHODS

Central FFAR1 agonism and virogenic knockdown were performed in mice. Energy balance studies, infrared thermographic analysis of brown adipose tissue (BAT) and molecular analysis of the hypothalamus, BAT, white adipose tissue (WAT) and liver were carried out.

RESULTS

Pharmacological stimulation of FFAR1, using central administration of its agonist TUG-905 in diet-induced obese mice, decreases body weight and is associated with increased energy expenditure, BAT thermogenesis and browning of subcutaneous WAT (sWAT), as well as reduced AMP-activated protein kinase (AMPK) levels, reduced inflammation, and decreased endoplasmic reticulum (ER) stress in the hypothalamus. As FFAR1 is expressed in distinct hypothalamic neuronal subpopulations, we used an AAV vector expressing a shRNA to specifically knockdown Ffar1 in proopiomelanocortin (POMC) neurons of the arcuate nucleus of the hypothalamus (ARC) of obese mice. Our data showed that knockdown of Ffar1 in POMC neurons promoted hyperphagia and body weight gain. In parallel, these mice developed hepatic insulin resistance and steatosis.

CONCLUSIONS

FFAR1 emerges as a new hypothalamic nutrient sensor regulating whole body energy balance. Moreover, pharmacological activation of FFAR1 could provide a therapeutic advance in the management of obesity and its associated metabolic disorders.

Beiging of perivascular adipose tissue regulates its inflammation and vascular remodeling

Although inflammation plays critical roles in the development of atherosclerosis, its regulatory mechanisms remain incompletely understood. Perivascular adipose tissue (PVAT) has been reported to undergo inflammatory changes in response to vascular injury. Here, we show that vascular injury induces the beiging (brown adipose tissue-like phenotype change) of PVAT, which fine-tunes inflammatory response and thus vascular remodeling as a protective mechanism. In a mouse model of endovascular injury, macrophages accumulate in PVAT, causing beiging phenotype change. Inhibition of PVAT beiging by genetically silencing PRDM16, a key regulator to beiging, exacerbates inflammation and vascular remodeling following injury. Conversely, activation of PVAT beiging attenuates inflammation and pathological vascular remodeling. Single-cell RNA sequencing reveals that beige adipocytes abundantly express neuregulin 4 (Nrg4) which critically regulate alternative macrophage activation. Importantly, significant beiging is observed in the diseased aortic PVAT in patients with acute aortic dissection. Taken together, vascular injury induces the beiging of adjacent PVAT with macrophage accumulation, where NRG4 secreted from the beige PVAT facilitates alternative activation of macrophages, leading to the resolution of vascular inflammation. Our study demonstrates the pivotal roles of PVAT in vascular inflammation and remodeling and will open a new avenue for treating atherosclerosis.

Perivascular adipose tissue (PVAT) has been reported to undergo inflammatory changes in response to vascular injury. Here, the authors show that vascular injury induces the beiging (brown adipose tissue-like phenotype change) of PVAT, which fine-tunes inflammatory response as a protective mechanism.

Emerging Pharmacological Targets for the Treatment of Nonalcoholic Fatty Liver Disease, Insulin Resistance, and Type 2 Diabetes

Type 2 diabetes (T2D) is characterized by persistent hyperglycemia despite hyperinsulinemia, affects more than 400 million people worldwide, and is a major cause of morbidity and mortality. Insulin resistance, of which ectopic lipid accumulation in the liver [nonalcoholic fatty liver disease (NAFLD)] and skeletal muscle is the root cause, plays a major role in the development of T2D. Although lifestyle interventions and weight loss are highly effective at reversing NAFLD and T2D, weight loss is difficult to sustain, and newer approaches aimed at treating the root cause of T2D are urgently needed. In this review, we highlight emerging pharmacological strategies aimed at improving insulin sensitivity and T2D by altering hepatic energy balance or inhibiting key enzymes involved in hepatic lipid synthesis. We also summarize recent research suggesting that liver-targeted mitochondrial uncoupling may be an attractive therapeutic approach to treat NAFLD, nonalcoholic steatohepatitis, and T2D.

An update on metabolic syndrome: Metabolic risk markers and adipokines in the development of metabolic syndrome

Metabolic syndrome is a collection of physiological and biochemical abnormalities about 20-25% of adult population in developing countries is suffering from metabolic syndrome. Previous research demonstrated that adipose tissue plays an important role in energy regulation via endocrine, paracrine and autocrine signals as results of obesity due to accumulation of adipose tissue to excess that by time affects negatively both physical and psychological health and well being, it has been found that adipose tissues produces a variety of factors known as "adipokines" which play a key role in the development and progression of the disease and also hypothesized that adipokines are a possible link between obesity and the other risk components of the Metabolic syndrome. Many of the adipokines exert multiple actions in a variety of cellular processes leading to a complex array of abnormal characteristic of Metabolic syndrome. Abnormal production of these adipokines by expanded visceral fat during Adiposity contributes to a pro-inflammatory state. Increasing evidence suggests that aberrant production/release of adipokine from adipocyte i.e. adiponectin, leptin and resistin etc, may contribute to the health problems associated with Adiposity such as dyslipidemia, insulin resistance and atherosclerosis. This study conclusively have shown a significant role of adipokines secreted by adipose tissue and various metabolic risk markers play a important role in the development of Metabolic syndrome.

Deletion of JNK2 prevents vitamin-D-deficiency-induced hypertension and atherosclerosis in mice

The c-Jun N-terminal kinase 2 (JNK2) signaling pathway contributes to inflammation and plays a key role in the development of obesity-induced insulin resistance and cardiovascular disease. Macrophages are key cells implicated in these metabolic abnormalities. Active vitamin D downregulates macrophage JNK activation, suppressing oxidized LDL cholesterol uptake and foam cell formation and promoting an anti-inflammatory phenotype. To determine whether deletion of JNK2 prevents high blood pressure and atherosclerosis known to be induced by vitamin D deficiency in mice, we generated mice with knockout of JNK2 in a background susceptible to diet-induced atherosclerosis (LDLR^-/-). JNK2^-/- LDLR^-/- and LDLR^-/- control mice were fed vitamin D-deficient chow for 8 weeks followed by vitamin D-deficient high fat diet (HFD) for 10 weeks and assessed before and after HFD. There was no difference in fasting glucose, cholesterol, triglycerides, or free fatty acid levels. However, JNK2^-/- mice, despite vitamin D-deficient diet, had 20-30mmHg lower systolic (SBP) and diastolic (DBP) blood pressure before HFD compared to control mice fed vitamin D-deficient diets, with persistent SBP differences after HFD. Moreover, deletion of JNK2 reduced HFD-induced atherosclerosis by 30% in the proximal aorta when compared to control mice fed vitamin D-deficient diets. We have previously shown that peritoneal macrophages obtained from LDLR^-/- mice fed vitamin D-deficient HFD diets have higher foam cell formation compared to those from mice on vitamin D-sufficient HFD. The increased total cellular cholesterol and modified cholesterol uptake in macrophages from mice on vitamin D-deficient HFD were blunted by deletion of JNK2. These data suggest that JNK2 signaling activation is necessary for the atherosclerosis and hypertension induced by vitamin D deficiency.

Electro-pharmacological profiles of two brain mitoplast anion channels: Inferences from single channel recording

We have characterized the conduction and blocking properties of two different chloride channels from brain mitochondrial inner membranes after incorporation into planar lipid bilayers. Our experiments revealed the existence of channels with a mean conductance of 158 ± 7 and 301 ± 8 pS in asymmetrical 200 mM cis/50 mM trans KCl solutions. We determined that the channels were ten times more permeable for Cl⁻ than for K⁺, calculated from the reversal potential using the Goldman-Hodgkin-Katz equation. The channels were bell-shaped voltage dependent, with maximum open probability 0.9 at ± 20 mV. Two mitochondrial chloride channels were blocked after the addition of 10 µM DIDS. In addition, 158 pS chloride channel was blocked by 300 nM NPPB, acidic pH and 2.5 mM ATP, whereas the 301 pS chloride channel was blocked by 600 µM NPPB but not by acidic pH or ATP. Gating and conducting behaviors of these channels were unaffected by Ca²⁺. These results demonstrate that the 158 pS anion channel present in brain mitochondrial inner membrane, is probably identical to IMAC and 301 pS Cl channel displays different properties than those classically described for mitochondrial anion channels.

Skeletal muscle mitochondrial uncoupling prevents diabetes but not obesity in NZO mice, a model for polygenic diabesity

Induction of skeletal muscle (SM) mitochondrial stress by expression of uncoupling protein 1 (UCP1) in mice results in a healthy metabolic phenotype associated with increased secretion of FGF21 from SM. Here, we investigated whether SM mitochondrial uncoupling can compensate obesity and insulin resistance in the NZO mouse, a polygenic diabesity model. Male NZO mice were crossed with heterozygous UCP1 transgenic (tg) mice (mixed C57BL/6/CBA background) and further backcrossed to obtain F1 and N2 offspring with 50 and 75 % NZO background, respectively. Male F1 and N2 progeny were fed a high-fat diet ad libitum for 20 weeks from weaning. Blood glucose was reduced, and diabetes (severe hyperglycemia >300 mg/dl) was fully prevented in both F1- and N2-tg progeny compared to a diabetes prevalence of 15 % in F1 and 42 % in N2 wild type. In contrast, relative body fat content and plasma insulin were decreased, and glucose tolerance was improved, in F1-tg only. Both F1 and N2-tg showed decreased lean body mass. Accordingly, induction of SM stress response including FGF21 expression and secretion was similar in both F1 and N2-tg mice. In white adipose tissue, expression of FGF21 target genes was enhanced in F1 and N2-tg mice, whereas lipid metabolism genes were induced in F1-tg only. There was no evidence for induction of browning in either UCP1 backcross. We conclude that SM mitochondrial uncoupling induces FGF21 expression and prevents diabetes in mice with a 50-75 % NZO background independent of its effects on adipose tissue.

New Insights for Oxidative Stress and Diabetes Mellitus

The release of reactive oxygen species (ROS) and the generation of oxidative stress are considered critical factors for the pathogenesis of diabetes mellitus (DM), a disorder that is growing in prevalence and results in significant economic loss. New therapeutic directions that address the detrimental effects of oxidative stress may be especially warranted to develop effective care for the millions of individuals that currently suffer from DM. The mechanistic target of rapamycin (mTOR), silent mating type information regulation 2 homolog 1 (S. cerevisiae) (SIRT1), and Wnt1 inducible signaling pathway protein 1 (WISP1) are especially justified to be considered treatment targets for DM since these pathways can address the complex relationship between stem cells, trophic factors, impaired glucose tolerance, programmed cell death pathways of apoptosis and autophagy, tissue remodeling, cellular energy homeostasis, and vascular biology that greatly impact the biology and disease progression of DM. The translation and development of these pathways into viable therapies will require detailed understanding of their proliferative nature to maximize clinical efficacy and limit adverse effects that have the potential to lead to unintended consequences.

Regulation of systemic energy homeostasis by serotonin in adipose tissues

Central serotonin (5-HT) is an anorexigenic neurotransmitter in the brain. However, accumulating evidence suggests peripheral 5-HT may affect organismal energy homeostasis. Here we show 5-HT regulates white and brown adipose tissue function. Pharmacological inhibition of 5-HT synthesis leads to inhibition of lipogenesis in epididymal white adipose tissue (WAT), induction of browning in inguinal WAT and activation of adaptive thermogenesis in brown adipose tissue (BAT). Mice with inducible Tph1 KO in adipose tissues exhibit a similar phenotype as mice in which 5-HT synthesis is inhibited pharmacologically, suggesting 5-HT has localized effects on adipose tissues. In addition, Htr3a KO mice exhibit increased energy expenditure and reduced weight gain when fed a high-fat diet. Treatment with an Htr2a antagonist reduces lipid accumulation in 3T3-L1 adipocytes. These data suggest important roles for adipocyte-derived 5-HT in controlling energy homeostasis.

Programming apoptosis and autophagy with novel approaches for diabetes mellitus

According to the World Health Organization, diabetes mellitus (DM) in the year 2030 will be ranked the seventh leading cause of death in the world. DM impacts all systems of the body with oxidant stress controlling cell fate through endoplasmic reticulum stress, mitochondrial dysfunction, alterations in uncoupling proteins, and the induction of apoptosis and autophagy. Multiple treatment approaches are being entertained for DM with Wnt1 inducible signaling pathway protein 1 (WISP1), mechanistic target of rapamycin (mTOR), and silent mating type information regulation 2 homolog) 1 (S. cerevisiae) (SIRT1) generating significant interest as target pathways that can address maintenance of glucose homeostasis as well as prevention of cellular pathology by controlling insulin resistance, stem cell proliferation, and the programmed cell death pathways of apoptosis and autophagy. WISP1, mTOR, and SIRT1 can rely upon similar pathways such as AMP activated protein kinase as well as govern cellular metabolism through cytokines such as EPO and oral hypoglycemics such as metformin. Yet, these pathways require precise biological control to exclude potentially detrimental clinical outcomes. Further elucidation of the ability to translate the roles of WISP1, mTOR, and SIRT1 into effective clinical avenues offers compelling prospects for new therapies against DM that can benefit hundreds of millions of individuals throughout the globe.

Muscle lipogenesis balances insulin sensitivity and strength through calcium signaling

Exogenous dietary fat can induce obesity and promote diabetes, but endogenous fat production is not thought to affect skeletal muscle insulin resistance, an antecedent of metabolic disease. Unexpectedly, the lipogenic enzyme fatty acid synthase (FAS) was increased in the skeletal muscle of mice with diet-induced obesity and insulin resistance. Skeletal muscle-specific inactivation of FAS protected mice from insulin resistance without altering adiposity, specific inflammatory mediators of insulin signaling, or skeletal muscle levels of diacylglycerol or ceramide. Increased insulin sensitivity despite high-fat feeding was driven by activation of AMPK without affecting AMP content or the AMP/ATP ratio in resting skeletal muscle. AMPK was induced by elevated cytosolic calcium caused by impaired sarco/endoplasmic reticulum calcium ATPase (SERCA) activity due to altered phospholipid composition of the sarcoplasmic reticulum (SR), but came at the expense of decreased muscle strength. Thus, inhibition of skeletal muscle FAS prevents obesity-associated diabetes in mice, but also causes muscle weakness, which suggests that mammals have retained the capacity for lipogenesis in muscle to preserve physical performance in the setting of disrupted metabolic homeostasis.

Vitamin D deficiency induces high blood pressure and accelerates atherosclerosis in mice

Multiple epidemiological studies link vitamin D deficiency to increased cardiovascular disease (CVD), but causality and possible mechanisms underlying these associations are not established. To clarify the role of vitamin D-deficiency in CVD in vivo, we generated mouse models of diet-induced vitamin D deficiency in two backgrounds (LDL receptor- and ApoE-null mice) that resemble humans with diet-induced hypertension and atherosclerosis. Mice were fed vitamin D-deficient or -sufficient chow for 6 weeks and then switched to high fat (HF) vitamin D-deficient or -sufficient diet for 8-10 weeks. Mice with diet-induced vitamin D deficiency showed increased systolic and diastolic blood pressure, high plasma renin, and decreased urinary sodium excretion. Hypertension was reversed and renin was suppressed by returning chow-fed vitamin D-deficient mice to vitamin D-sufficient chow diet for 6 weeks. On a HF diet, vitamin D-deficient mice had ~2-fold greater atherosclerosis in the aortic arch and ~2-8-fold greater atherosclerosis in the thoracic and abdominal aorta compared to vitamin D-sufficient mice. In the aortic root, HF-fed vitamin D-deficient mice had increased macrophage infiltration with increased fat accumulation and endoplasmic reticulum (ER) stress activation, but a lower prevalence of the M1 macrophage phenotype within atherosclerotic plaques. Similarly, peritoneal macrophages from vitamin D-deficient mice displayed an M2-predominant phenotype with increased foam cell formation and ER stress. Treatment of vitamin D-deficient mice with the ER stress reliever PBA during HF feeding suppressed atherosclerosis, decreased peritoneal macrophage foam cell formation, and downregulated ER stress proteins without changing blood pressure. Thus, we suggest that vitamin D deficiency activates both the renin angiotensin system and macrophage ER stress to contribute to the development of hypertension and accelerated atherosclerosis, highlighting vitamin D replacement as a potential therapy to reduce blood pressure and atherosclerosis.

Importance of β-Catenin in glucose and energy homeostasis

In settings of increased insulin demand, failure to expand pancreatic β-cells mass leads to diabetes. Genome-wide scans of diabetic populations have uncovered several genes associated with susceptibility to type 2 diabetes and a number of them are part of the Wnt signaling. β-Catenin, a Wnt downstream effector participates in pancreatic development, however, little is known about its action in mature β-cells. Deletion of β-Catenin in Pdx1 pancreatic progenitors leads to a decreased β-cell mass and impaired glucose tolerance. Surprisingly, loss of β-catenin made these mice resistant to high fat diet because of their increased energy expenditure and insulin sensitivity due to hyperactivity. The complexity of this phenotype was also explained in part by ectopic expression of Cre recombinase in the hypothalamus. Our data implicates β-Catenin in the regulation of metabolism and energy homeostasis and suggest that Wnt signaling modulates the susceptibility to diabetes by acting on different tissues.

Augmenting energy expenditure by mitochondrial uncoupling: a role of AMP-activated protein kinase

Strategies to prevent and treat obesity aim to decrease energy intake and/or increase energy expenditure. Regarding the increase of energy expenditure, two key intracellular targets may be considered (1) mitochondrial oxidative phosphorylation, the major site of ATP production, and (2) AMP-activated protein kinase (AMPK), the master regulator of cellular energy homeostasis. Experiments performed mainly in transgenic mice revealed a possibility to ameliorate obesity and associated disorders by mitochondrial uncoupling in metabolically relevant tissues, especially in white adipose tissue (WAT), skeletal muscle (SM), and liver. Thus, ectopic expression of brown fat-specific mitochondrial uncoupling protein 1 (UCP1) elicited major metabolic effects both at the cellular/tissue level and at the whole-body level. In addition to expected increases in energy expenditure, surprisingly complex phenotypic effects were detected. The consequences of mitochondrial uncoupling in WAT and SM are not identical, showing robust and stable obesity resistance accompanied by improvement of lipid metabolism in the case of ectopic UCP1 in WAT, while preservation of insulin sensitivity in the context of high-fat feeding represents the major outcome of muscle UCP1 expression. These complex responses could be largely explained by tissue-specific activation of AMPK, triggered by a depression of cellular energy charge. Experimental data support the idea that (1) while being always activated in response to mitochondrial uncoupling and compromised intracellular energy status in general, AMPK could augment energy expenditure and mediate local as well as whole-body effects; and (2) activation of AMPK alone does not lead to induction of energy expenditure and weight reduction.

Association of the sirtuin and mitochondrial uncoupling protein genes with carotid plaque

Objective

Sirtuins (SIRTs) and mitochondrial uncoupling proteins (UCPs) have been implicated in cardiovascular diseases through the control of reactive oxygen species production. This study sought to investigate the association between genetic variants in the SIRT and UCP genes and carotid plaque.

Methods

In a group of 1018 stroke-free subjects from the Northern Manhattan Study with high-definition carotid ultrasonography and genotyping, we investigated the associations of 85 single nucleotide polymorphisms (SNPs) in the 11 SIRT and UCP genes with the presence and number of carotid plaques, and evaluated interactions of SNPs with sex, smoking, diabetes and hypertension as well as interactions between SNPs significantly associated with carotid plaque.

Results

Overall, 60% of subjects had carotid plaques. After adjustment for demographic and vascular risk factors, T-carriers of the SIRT6 SNP rs107251 had an increased risk for carotid plaque (odds ratio, OR = 1.71, 95% CI = 1.23–2.37, Bonferroni-corrected p = 0.03) and for a number of plaques (rate ratio, RR = 1.31, 1.18–1.45, Bonferroni-corrected p = 1.4×10⁻⁵), whereas T-carriers of the UCP5 SNP rs5977238 had an decreased risk for carotid plaque (OR = 0.49, 95% CI = 0.32–0.74, Bonferroni-corrected p = 0.02) and plaque number (RR = 0.64, 95% CI = 0.52–0.78, Bonferroni-corrected p = 4.9×10⁻⁴). Some interactions with a nominal p≤0.01 were found between sex and SNPs in the UCP1 and UCP3 gene; between smoking, diabetes, hypertension and SNPs in UCP5 and SIRT5; and between SNPs in the UCP5 gene and the UCP1, SIRT1, SIRT3, SIRT5, and SIRT6 genes in association with plaque phenotypes.

Conclusion

We observed significant associations between genetic variants in the SIRT6 and UCP5 genes and atherosclerotic plaque. We also found potential effect modifications by sex, smoking and vascular risk factors of the SIRT/UCP genes in the associations with atherosclerotic plaque. Further studies are needed to validate our observations.

The mitochondrial paradigm for cardiovascular disease susceptibility and cellular function: a complementary concept to Mendelian genetics

While there is general agreement that cardiovascular disease (CVD) development is influenced by a combination of genetic, environmental, and behavioral contributors, the actual mechanistic basis of how these factors initiate or promote CVD development in some individuals while others with identical risk profiles do not, is not clearly understood. This review considers the potential role for mitochondrial genetics and function in determining CVD susceptibility from the standpoint that the original features that molded cellular function were based upon mitochondrial-nuclear relationships established millions of years ago and were likely refined during prehistoric environmental selection events that today, are largely absent. Consequently, contemporary risk factors that influence our susceptibility to a variety of age-related diseases, including CVD were probably not part of the dynamics that defined the processes of mitochondrial-nuclear interaction, and thus, cell function. In this regard, the selective conditions that contributed to cellular functionality and evolution should be given more consideration when interpreting and designing experimental data and strategies. Finally, future studies that probe beyond epidemiologic associations are required. These studies will serve as the initial steps for addressing the provocative concept that contemporary human disease susceptibility is the result of selection events for mitochondrial function that increased chances for prehistoric human survival and reproductive success.

Dietary effects on body composition, glucose metabolism, and longevity are modulated by skeletal muscle mitochondrial uncoupling in mice

Little is known about how diet and energy metabolism interact in determination of lifespan under ad libitum feeding. From 12 weeks of age until death, male and female wild-type (WT) and transgenic (TG) mice with increased skeletal muscle mitochondrial uncoupling (HSA-mUCP1 mice) were fed one of three different semisynthetic diets differing in macronutrient ratio: control (high-carbohydrate/low-fat-HCLF) and two high-fat diets: high-carbohydrate/high-fat (HCHF), and low-carbohydrate/high-fat (LCHF). Compared to control and LCHF, HCHF feeding rapidly and significantly increased body fat content in WT. Median lifespan of WT was decreased by 33% (HCHF) and 7% (LCHF) compared to HCLF. HCHF significantly increased insulin resistance (HOMA) of WT from 24 weeks on compared to control. TG mice had lower lean body mass and increased energy expenditure, insulin sensitivity, and maximum lifespan (+10%) compared to WT. They showed a delayed development of obesity on HCHF but reached similar maximum adiposity as WT. TG median lifespan was only slightly reduced by HCHF (−7%) and unaffected by LCHF compared to control. Correlation analyses showed that decreased longevity was more strongly linked to a high rate of fat gain than to adiposity itself. Furthermore, insulin resistance was negatively and weight-specific energy expenditure was positively correlated with longevity. We conclude that (i) dietary macronutrient ratios strongly affected obesity development, glucose homeostasis, and longevity, (ii) that skeletal muscle mitochondrial uncoupling alleviated the detrimental effects of high-fat diets, and (iii) that early imbalances in energy homeostasis leading to increased insulin resistance are predictive for a decreased lifespan.

Loss of Par-1a/MARK3/C-TAK1 kinase leads to reduced adiposity, resistance to hepatic steatosis, and defective gluconeogenesis

Par-1 is an evolutionarily conserved protein kinase required for polarity in worms, flies, frogs, and mammals. The mammalian Par-1 family consists of four members. Knockout studies of mice implicate Par-1b/MARK2/EMK in regulating fertility, immune homeostasis, learning, and memory as well as adiposity, insulin hypersensitivity, and glucose metabolism. Here, we report phenotypes of mice null for a second family member (Par-1a/MARK3/C-TAK1) that exhibit increased energy expenditure, reduced adiposity with unaltered glucose handling, and normal insulin sensitivity. Knockout mice were protected against high-fat diet-induced obesity and displayed attenuated weight gain, complete resistance to hepatic steatosis, and improved glucose handling with decreased insulin secretion. Overnight starvation led to complete hepatic glycogen depletion, associated hypoketotic hypoglycemia, increased hepatocellular autophagy, and increased glycogen synthase levels in Par-1a(-/-) but not in control or Par-1b(-/-) mice. The intercrossing of Par-1a(-/-) with Par-1b(-/-) mice revealed that at least one of the four alleles is necessary for embryonic survival. The severity of phenotypes followed a rank order, whereby the loss of one Par-1b allele in Par-1a(-/-) mice conveyed milder phenotypes than the loss of one Par-1a allele in Par-1b(-/-) mice. Thus, although Par-1a and Par-1b can compensate for one another during embryogenesis, their individual disruption gives rise to distinct metabolic phenotypes in adult mice.

Deletion of Tis7 protects mice from high-fat diet-induced weight gain and blunts the intestinal adaptive response postresection

After loss of intestinal surface area, the remaining bowel undergoes a morphometric and functional adaptive response. Enterocytic expression of the transcriptional coregulator tetradecanoyl phorbol acetate induced sequence 7 (Tis7) is markedly increased in a murine model of intestinal adaptation. Mice overexpressing Tis7 in intestine have greater triglyceride absorption and weight gain when fed a high-fat diet (42% energy) than their wild-type (WT) littermates fed the same diet. These and other data suggest that Tis7 has a unique role in nutrient absorptive and metabolic adaptation. Herein, male Tis7(-/-) and WT mice were fed a high-fat diet (42% energy) for 8 wk. Weight was monitored and metabolic analyses and hepatic and intestinal lipid concentrations were compared after 8 wk. Intestinal lipid absorption and metabolism studies and intestinal resection surgeries were performed in separate groups of Tis7(-/-) and WT mice. At 8 wk, weight gain was less and jejunal mucosal and hepatic triglyceride and cholesterol concentrations were lower in Tis7(-/-) mice than in the WT controls. Following corn oil gavage, serum cholesterol, triglyceride, and FFA concentrations were lower in the Tis7(-/-) mice than in the WT mice. Incorporation of oral (3)[H] triolein into intestinal mucosal cholesterol ester and FFA was less in Tis7(-/-) compared with WT mice. Following resection, crypt cell proliferation rates and villus heights were lower in Tis7(-/-) than in WT mice, indicating a blunted adaptive response. Our results suggest a novel physiologic function for Tis7 in the gut as a global regulator of lipid absorption and metabolism and epithelial cell proliferation.

Mice deficient in group VIB phospholipase A2 (iPLA2gamma) exhibit relative resistance to obesity and metabolic abnormalities induced by a Western diet

Phospholipases A(2) (PLA(2)) play important roles in metabolic processes, and the Group VI PLA(2) family is comprised of intracellular enzymes that do not require Ca(2+) for catalysis. Mice deficient in Group VIA PLA(2) (iPLA(2)beta) develop more severe glucose intolerance than wild-type (WT) mice in response to dietary stress. Group VIB PLA(2) (iPLA(2)gamma) is a related enzyme distributed in membranous organelles, including mitochondria, and iPLA(2)gamma knockout (KO) mice exhibit altered mitochondrial morphology and function. We have compared metabolic responses of iPLA(2)gamma-KO and WT mice fed a Western diet (WD) with a high fat content. We find that KO mice are resistant to WD-induced increases in body weight and adiposity and in blood levels of cholesterol, glucose, and insulin, even though WT and KO mice exhibit similar food consumption and dietary fat digestion and absorption. KO mice are also relatively resistant to WD-induced insulin resistance, glucose intolerance, and altered patterns of fat vs. carbohydrate fuel utilization. KO skeletal muscle exhibits impaired mitochondrial beta-oxidation of fatty acids, as reflected by accumulation of larger amounts of long-chain acylcarnitine (LCAC) species in KO muscle and liver compared with WT in response to WD feeding. This is associated with increased urinary excretion of LCAC and much reduced deposition of triacylglycerols in liver by WD-fed KO compared with WT mice. The iPLA(2)gamma-deficient genotype thus results in a phenotype characterized by impaired mitochondrial oxidation of fatty acids and relative resistance to the metabolic abnormalities induced by WD.

Macrophage fatty-acid synthase deficiency decreases diet-induced atherosclerosis

Fatty acid metabolism is perturbed in atherosclerotic lesions, but whether it affects lesion formation is unknown. To determine whether fatty acid synthesis affects atherosclerosis, we inactivated fatty-acid synthase (FAS) in macrophages of apoE-deficient mice. Serum lipids, body weight, and glucose metabolism were the same in FAS knock-out in macrophages (FASKOM) and control mice, but blood pressure was lower in FASKOM animals. Atherosclerotic extent was decreased 20-40% in different aortic regions of FASKOM as compared with control mice on Western diets. Foam cell formation was diminished in FASKOM as compared with wild type macrophages due to increased apoAI-specific cholesterol efflux and decreased uptake of oxidized low density lipoprotein. Expression of the anti-atherogenic nuclear receptor liver X receptor alpha (LXRalpha; Nr1h3) and its downstream targets, including Abca1, were increased in FASKOM macrophages, whereas expression of the potentially pro-atherogenic type B scavenger receptor CD36 was decreased. Peroxisome proliferator-activated receptor alpha (PPARalpha) target gene expression was decreased in FASKOM macrophages. PPARalpha agonist treatment of FASKOM and wild type macrophages normalized PPARalpha target gene expression as well as Nr1h3 (LXRalpha). Atherosclerotic lesions were more extensive when apoE null mice were transplanted with LXRalpha-deficient/FAS-deficient bone marrow as compared with LXRalpha-replete/FAS-deficient marrow, consistent with anti-atherogenic effects of LXRalpha in the context of FAS deficiency. These results show that macrophage FAS deficiency decreases atherosclerosis through induction of LXRalpha and suggest that FAS, which is induced by LXRalpha, may generate regulatory lipids that cause feedback inhibition of LXRalpha in macrophages.

Compromised respiratory adaptation and thermoregulation in aging and age-related diseases

Mitochondrial dysfunction and reactive oxygen species (ROS) production are at the heart of the aging process and are thought to underpin age-related diseases. Mitochondria are not only the primary energy-generating system but also the dominant cellular source of metabolically derived ROS. Recent studies unravel the existence of mechanisms that serve to modulate the balance between energy metabolism and ROS production. Among these is the regulation of proton conductance across the inner mitochondrial membrane that affects the efficiency of respiration and heat production. The field of mitochondrial respiration research has provided important insight into the role of altered energy balance in obesity and diabetes. The notion that respiration and oxidative capacity are mechanistically linked is making significant headway into the field of aging and age-related diseases. Here we review the regulation of cellular energy and ROS balance in biological systems and survey some of the recent relevant studies that suggest that respiratory adaptation and thermodynamics are important in aging and age-related diseases.

Yeast protein-surfactant complexes uncouple microbial electron transfer and increase transmembrane leak of protons

AIMS

To explore the combined effect of yeast proteins and surfactants on bacterial metabolism.

METHODS AND RESULTS

Protein-rich cell-free supernatant from heat-shocked yeast Saccharomyces cerevisiae was combined with certain synthetic surfactants. These blends affected the metabolism of a Polyseed inoculum of aerobic bacteria, accelerating CO(2) production and consumption of nutrients from a sterile nutrient broth solution, without a concomitant accumulation of biomass. It is suggested that in the presence of the yeast protein-surfactant complexes, bacterial electron transport is uncoupled from biomass accumulation. The 'uncoupling hypothesis' is supported by experiments with model membranes, in which the same complexes induced proton leak similar to standard chemical uncouplers, such as dinitrophenol, indicating that uncoupling may occur at the stage of generation of the transmembrane pH gradient as the driving force for ATP production.

CONCLUSIONS

Yeast protein-surfactant complexes behave as uncouplers of oxidative metabolism in bacteria and appear to do so by increasing proton permeability of membranes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Yeast proteins may be of interest as nontoxic, environmentally benign and economically sound agents accelerating oxidative bacterial metabolism while uncoupling it from biomass accumulation. There are actual and potential implications in waste water/soil decontamination, degreasing and other environmental technologies.

The metabolic syndrome

The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.

Association of UCP1 genetic polymorphisms with blood pressure among Korean female subjects

Recent studies have provided some clues with regard to the relationship existing between uncoupling protein 1 (UCP1) and blood pressure in animal experiments. In an attempt to determine the genetic polymorphisms that are associated with blood pressure in humans, we have analyzed genetic polymorphisms in UCP1 gene. In this study, we assessed the association between UCP1 genotypes and systolic blood pressure (SBP) and diastolic blood pressure (DBP), in a population comprised of 832 Korean female subjects, using a general linear model, which was adjusted for age and body mass index (BMI). Among 4 genetic polymorphisms and the haplotypes constructed from them, haplotype3 of UCP1, UCP1-ht3[GAGA], evidenced significant associations with SBP (p=0.005) and DBP (p=0.013). However, this haplotype was not significantly associated with obesity phenotypes, including BMI or fat mass (p>0.05), thereby suggesting that its association with blood pressure was independent of obesity phenotypes.

Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome

We have investigated the interrelationship between diet, gut microbial ecology, and energy balance using a mouse model of obesity produced by consumption of a prototypic Western diet. Diet-induced obesity (DIO) produced a bloom in a single uncultured clade within the Mollicutes class of the Firmicutes, which was diminished by subsequent dietary manipulations that limit weight gain. Microbiota transplantation from mice with DIO to lean germ-free recipients promoted greater fat deposition than transplants from lean donors. Metagenomic and biochemical analysis of the gut microbiome together with sequencing and metabolic reconstructions of a related human gut-associated Mollicute (Eubacterium dolichum) revealed features that may provide a competitive advantage to members of the bloom in the Western diet nutrient milieu, including import and processing of simple sugars. Our study illustrates how combining comparative metagenomics with gnotobiotic mouse models and specific dietary manipulations can disclose the niches of previously uncharacterized members of the gut microbiota.

Respiratory uncoupling in skeletal muscle delays death and diminishes age-related disease

Age-related disease, not aging per se, causes most morbidity in older humans. Here we report that skeletal muscle respiratory uncoupling due to UCP1 expression diminishes age-related disease in three mouse models. In a longevity study, median survival was increased in UCP mice (animals with skeletal muscle-specific UCP1 expression), and lymphoma was detected less frequently in UCP female mice. In apoE null mice, a vascular disease model, diet-induced atherosclerosis was decreased in UCP animals. In agouti yellow mice, a genetic obesity model, diabetes and hypertension were reversed by induction of UCP1 in skeletal muscle. Uncoupled mice had decreased adiposity, increased temperature and metabolic rate, elevated muscle SIRT and AMP kinase, and serum characterized by increased adiponectin and decreased IGF-1 and fibrinogen. Accelerating metabolism in skeletal muscle does not appear to impact aging but may delay age-related disease.

c-Kit in early onset of diabetes: a morphological and functional analysis of pancreatic beta-cells in c-KitW-v mutant mice

c-Kit tyrosine receptor kinase, a well-established stem cell marker, is expressed in a variety of tissues including the pancreas. The involvement of c-Kit in fetal rat and human endocrine pancreatic development, survival, and function has been well characterized but primarily using in vitro experimental approaches. Therefore, the aim of the current study was to examine whether deficiency of a functional c-Kit receptor would have physiological and functional implications in vivo. We characterized the c-Kit mutant mouse, c-Kit(W-v/+), to evaluate the in vivo role of c-Kit in beta-cell growth and function. Here we report that male c-Kit(W-v/+) mice, at 8 wk of age, showed high fasting blood glucose levels and impaired glucose tolerance, which was associated with low levels of insulin secretion after glucose stimulation in vivo and in isolated islets. Morphometric analysis revealed that beta-cell mass was significantly reduced (50%) in male c-Kit(W-v/+) mice when compared with controls (c-Kit(+/+)) (P < 0.05). In parallel, a reduction in pancreatic duodenal homeobox-1 and insulin gene expression in whole pancreas as well as isolated islets of c-Kit(W-v/+) male mice was noted along with a decrease in pancreatic insulin content. Furthermore, the reduction in beta-cell mass in male c-Kit(W-v/+) mice was associated with a decrease in beta-cell proliferation. Interestingly, these changes were not observed in female c-Kit(W-v/+) mice until 40 wk of age. Our results clearly demonstrate that the c-Kit receptor is involved in the regulation of glucose metabolism, likely through an important role in beta-cell development and function.

Lysosomal dysfunction results in altered energy balance

The mucopolysaccharidosis (MPS) type VII mouse was originally described as the adipose storage deficiency mouse because of its extreme lean phenotype of unknown etiology. Here, we show that adipose storage deficiency and lower leptin levels are common to five different lysosomal storage diseases (LSDs): MPSI, MPSIIIB, MPSVII, Niemann-Pick type A/B, and infantile neuronal ceroid lipofuscinosis. Elevated circulating pro-inflammatory proteins (VCAM1 and MCP1) were found in multiple LSDs. Multiple anti-inflammatory strategies (dexamethasone, MCP1 deficiency, M3 expression) failed to alter adiposity in LSD animals. All of the models had normal or greater caloric intake and lower to normal metabolic rate, fasting plasma glucose, non-esterified fatty acids, cholesterol, and triglycerides. Triglycerides were lower in the livers of MPSI mice, and the trend was lower in the muscle. Lipid absorption and processing in MPSI mice were indistinguishable from those in normal mice following oral gavage of olive oil. The increased lean mass of MPSI and MPSIIIB mice suggests a shift in adipose triglycerides to lysosomal storage. In agreement, MPSI livers had a similar total caloric content but reduced caloric density, indicating a shift in energy from lipids to proteins/carbohydrates (lysosomal storage). Enzyme replacement therapy normalized the caloric density within 48 h without reducing total caloric content. This was due to an increase in lipids. Recycling of stored material is likely reduced or nonexistent. Therefore, to maintain homeostasis, energy is likely diverted to synthesis at the expense of typical energy storage depots. Thus, these diseases will serve as important tools in studying the role of lysosome function in metabolism and obesity.

Genes, fat intake, and cardiovascular disease risk factors in the Quebec Family Study

OBJECTIVE

The aim of this study was to assess gene-diet interaction effects on cardiovascular disease (CVD) risk factors (waist circumference, plasma triacylglycerol, high-density lipoprotein-cholesterol and fasting glucose concentrations, and diastolic and systolic blood pressure) in the Quebec Family Study cohort.

DESIGN

Sixty-four polymorphisms from 45 candidate genes were studied in 645 subjects. Dietary fat intake was obtained from a 3-day weighted food record.

RESULTS

We observed 18 significant interactions at a p value <or= 0.01. Among them, the Pro12Ala polymorphism in peroxisome proliferator-activated receptor gamma, alone or in interaction with fat intake, significantly modulated waist circumference (p = 0.0005 for both effects). Additionally, the apolipoprotein E genotype in interaction with fat intake was significantly associated with diastolic and systolic blood pressure (p = 0.01 and p = 0.001, respectively). The ghrelin Leu72Met polymorphism also interacted with dietary fat in its relation to waist circumference and triacylglycerol concentrations (p = 0.0004 and p = 0.005).

DISCUSSION

These results suggest that several alleles at candidate genes interact with dietary fat intake to modulate well-known CVD risk factors. The identification of gene-diet interaction effects is likely to provide useful information concerning the etiology of CVD.

Oxidative stress biology and cell injury during type 1 and type 2 diabetes mellitus

Diabetes mellitus (DM) affects approximately 170 million individuals worldwide and is expected to alter the lives of at least 366 million individuals within a future span of 25 years. Of even greater concern is the premise that these projections are underestimated since they assume obesity levels will remain constant. Type 1 insulin-dependent DM accounts for only 5-10 percent of all diabetics but represents a highly significant health concern, since this disorder begins early in life and leads to long-term complications. In contrast, Type 2 DM is recognized as the etiology of over 80 percent of all diabetics and is dramatically increasing in incidence as a result of changes in human behavior and increased body mass index. Yet, the pathological consequences of these disorders that involve the both the neuronal and vascular systems are intimately linked through the pathways that mediate oxidative stress. Here we highlight some of the relevant oxidative pathways that determine insulin resistance through reactive oxygen species, mitochondrial dysfunction, uncoupling proteins, and endoplasmic reticulum stress. These pathways are ultimately linked to protein kinase B (Akt) and the insulin signaling pathways that determine the initial onset of glucose intolerance and the subsequent course to apoptotic cell injury. Through the elucidation of these targets, improvement in current strategies as well as the development of future clinical applications can move forward for both the prevention and treatment of Type 1 and Type 2 DM.

The role of tobacco smoke induced mitochondrial damage in vascular dysfunction and atherosclerosis

The majority of individuals chronically exposed to tobacco smoke will eventually succumb to cardiovascular disease (CVD). However, despite the major cardiovascular health implications of tobacco smoke exposure, concepts of how such exposure specifically results in cardiovascular cell dysfunction that leads to CVD development are still being explored. Moreover, surprisingly little is known about the effects of prenatal and childhood tobacco smoke exposure on adult CVD development. Herein, it is proposed that the mitochondrion is a central target for environmental oxidants, including tobacco smoke. By virtue of its multiple, essential roles in cell function including energy production, oxidant signaling, apoptosis, immune response, and thermogenesis, damage to the mitochondrion will likely play an important role in the development of multiple common forms of human disease, including CVD. Specifically, this review will discuss the potential role of tobacco smoke and environmental oxidant exposure in the induction of mitochondrial damage which is related to CVD development. Furthermore, mechanisms of how mitochondrial damage can initiate and/or contribute to CVD are discussed, as are experimental results that are consistent with the hypothesis that mitochondrial damage and dysfunction will increase CVD susceptibility. Aspects of both adult and developmental (fetal and childhood) exposure to tobacco smoke on mitochondrial damage, function and disease development are also discussed, including the future implications and direction of studies involving the role of the mitochondrion in influencing disease susceptibility mediated by environmental factors.

An afferent vagal nerve pathway links hepatic PPARalpha activation to glucocorticoid-induced insulin resistance and hypertension

Glucocorticoid excess causes insulin resistance and hypertension. Hepatic expression of PPARalpha (Ppara) is required for glucocorticoid-induced insulin resistance. Here we demonstrate that afferent fibers of the vagus nerve interface with hepatic Ppara expression to disrupt blood pressure and glucose homeostasis in response to glucocorticoids. Selective hepatic vagotomy decreased hyperglycemia, hyperinsulinemia, hepatic insulin resistance, Ppara expression, and phosphoenolpyruvate carboxykinase (PEPCK) enzyme activity in dexamethasone-treated Ppara(+/+) mice. Selective vagotomy also decreased blood pressure, adrenergic tone, renin activity, and urinary sodium retention in these mice. Hepatic reconstitution of Ppara in nondiabetic, normotensive dexamethasone-treated PPARalpha null mice increased glucose, insulin, hepatic PEPCK enzyme activity, blood pressure, and renin activity in sham-operated animals but not hepatic-vagotomized animals. Disruption of vagal afferent fibers by chemical or surgical means prevented glucocorticoid-induced metabolic derangements. We conclude that a dynamic interaction between hepatic Ppara expression and a vagal afferent pathway is essential for glucocorticoid induction of diabetes and hypertension.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

Leptin regulates neointima formation after arterial injury through mechanisms independent of blood pressure and the leptin receptor/STAT3 signaling pathways involved in energy balance

BACKGROUND

Leptin is an adipocyte-derived hormone critical for energy homeostasis and implicated in vascular disease processes. The relevant cellular leptin receptor pools and signaling pathways involved in leptin-related vascular phenotypes in vivo are unclear.

METHODS AND RESULTS

Arterial injury was induced in wild-type (wt), leptin-deficient (lep(ob/ob)), and leptin receptor-deficient (lepr(db/db)) mice. Compared with wt mice, lep(ob/ob) and lepr(db/db) mice were protected from the development of neointima. Bone marrow transplantation experiments between wt and lepr(db/db) mice indicated that the vascular protection in lepr(db/db) mice was not attributable to lack of leptin receptor expression on bone marrow-derived elements. To investigate the role of the lepr-mediated signal transducer and activator of transcription 3 (STAT3) signaling pathway in the response to vascular injury, lepr(s/s) mice homozygous for a leptin receptor defective in STAT3 signaling underwent femoral arterial injury. Despite similar obesity and blood pressure levels, the neointimal area in lepr(s/s) mice was significantly increased compared with lepr(db/db) mice.

CONCLUSIONS

The molecular mechanism by which the leptin receptor mediates neointima formation and vascular smooth muscle cell proliferation is largely independent of the STAT3-dependent signaling pathways involved in energy balance.

Respiration under control of uncoupling proteins: Clinical perspective

The term 'uncoupling protein' was originally used for the mitochondrial membrane protein UCP1, which is uniquely present in mitochondria of brown adipocytes, thermogenic cells that regulate body temperature in small rodents, hibernators and mammalian newborns. In these cells, UCP1 acts as a proton carrier activated by free fatty acids and creates a shunt between complexes of the respiratory chain and ATP-synthase resulting in a futile proton cycling and dissipation of oxidation energy as heat. Recent identification of new homologues to UCP1 expressed in brown and white adipose tissue, muscle, brain and other tissues together with the hypothesis that these novel uncoupling proteins (UCPs) may regulate thermogenesis and/or fatty acid metabolism and furthermore may protect against free radical oxygen species production have generated considerable optimism for rapid advances in the identification of new targets for pharmacological management of complex pathological syndromes such as obesity, type 2 diabetes or chronic inflammatory diseases. However, since the physiological and biochemical roles of the novel UCPs are not yet clear, the main challenge today consists first of all in providing mechanistic explanation for their functions in cellular physiology. This lively awaited information may be the basis for potential pharmacological targeting of the UCPs in future.

Insulin resistance and atherosclerosis

Considerable evidence supports the association between insulin resistance and vascular disease, and this has led to wide acceptance of the clustering of hyperlipidemia, glucose intolerance, hypertension, and obesity as a clinical entity, the metabolic syndrome. While insulin resistance, by promoting dyslipidemia and other metabolic abnormalities, is part of the proatherogenic milieu, it is possible that insulin resistance itself in the vascular wall does not promote atherosclerosis. Recent findings suggest that insulin resistance and atherosclerosis could represent independent and ultimately maladaptive responses to the disruption of cellular homeostasis caused by the excess delivery of fuel.

A humanized gnotobiotic mouse model of host-archaeal-bacterial mutualism

Our colons harbor trillions of microbes including a prominent archaeon, Methanobrevibacter smithii. To examine the contributions of Archaea to digestive health, we colonized germ-free mice with Bacteroides thetaiotaomicron, an adaptive bacterial forager of the polysaccharides that we consume, with or without M. smithii or the sulfate-reducing bacterium Desulfovibrio piger. Whole-genome transcriptional profiling of B. thetaiotaomicron, combined with mass spectrometry, revealed that, unlike D. piger, M. smithii directs B. thetaiotaomicron to focus on fermentation of dietary fructans to acetate, whereas B. thetaiotaomicron-derived formate is used by M. smithii for methanogenesis. B. thetaiotaomicron-M. smithii cocolonization produces a significant increase in host adiposity compared with monoassociated, or B. thetaiotaomicron-D. piger biassociated, animals. These findings demonstrate a link between this archaeon, prioritized bacterial utilization of polysaccharides commonly encountered in our modern diets, and host energy balance.

Bioenergetics of aging and calorie restriction

Aging is a physiological process that involves a multi-factorial set of deleterious changes. These alterations are caused by an exponential increase in damage to macromolecules. This process is likely due to the cumulative effects of oxidative stress over time. One area of ongoing research in gerontology has focused on determining why there is an age-dependent decrease in cellular bioenergetics. The aim of this review is to summarize the recent findings on the effects of aging and calorie restriction on energy metabolism. The effect of calorie restriction on age-associated changes in bioenergetic parameters will be examined.

Role of leptin in blood pressure regulation and arterial hypertension

Leptin is a 16-kDa protein secreted by white adipose tissue that is primarily involved in the regulation of food intake and energy expenditure. Plasma leptin concentration is proportional to the amount of adipose tissue and is markedly increased in obese individuals. Recent studies suggest that leptin is involved in cardiovascular complications of obesity, including arterial hypertension. Acutely administered leptin has no effect on blood pressure, probably because it concomitantly stimulates the sympathetic nervous system and counteracting depressor mechanisms such as natriuresis and nitric oxide (NO)-dependent vasorelaxation. By contrast, chronic hyperleptinemia increases blood pressure because these acute depressor effects are impaired and/or additional sympathetic nervous system-independent pressor effects appear, such as oxidative stress, NO deficiency, enhanced renal Na reabsorption and overproduction of endothelin. Although the cause-effect relationship between leptin and high blood pressure in humans has not been demonstrated directly, many clinical studies have shown elevated plasma leptin in patients with essential hypertension and a significant positive correlation between leptin and blood pressure independent of body adiposity both in normotensive and in hypertensive individuals. In addition, leptin may contribute to end-organ damage in hypertensive individuals such as left ventricular hypertrophy, retinopathy and nephropathy, independent of regulating blood pressure. Here, current knowledge about the role of leptin in the regulation of blood pressure and in the pathogenesis of arterial hypertension is presented.

Dinitrophenol-induced mitochondrial uncoupling in vivo triggers respiratory adaptation in HepG2 cells

Here, we show that 3 days of mitochondrial uncoupling, induced by low concentrations of dinitrophenol (10 and 50 microM) in cultured human HepG2 cells, triggers cellular metabolic adaptation towards oxidative metabolism. Chronic respiratory uncoupling of HepG2 cells induced an increase in cellular oxygen consumption, oxidative capacity and cytochrome c oxidase activity. This was associated with an upregulation of COXIV and ANT3 gene expression, two nuclear genes that encode mitochondrial proteins involved in oxidative phosphorylation. Glucose consumption, lactate and pyruvate production and growth rate were unaffected, indicating that metabolic adaptation of HepG2 cells undergoing chronic respiratory uncoupling allows continuous and efficient mitochondrial ATP production without the need to increase glycolytic activity. In contrast, 3 days of dinitrophenol treatment did not change the oxidative capacity of human 143B.TK(-) cells, but it increased glucose consumption, lactate and pyruvate production. Despite a large increase in glycolytic metabolism, the growth rate of 143B.TK(-) cells was significantly reduced by dinitrophenol-induced mitochondrial uncoupling. We propose that chronic respiratory uncoupling may constitute an internal bioenergetic signal, which would initiate a coordinated increase in nuclear respiratory gene expression, which ultimately drives mitochondrial metabolic adaptation within cells.

Antioxidant treatment normalizes nitric oxide production, renal sodium handling and blood pressure in experimental hyperleptinemia

Recent studies suggest that adipose tissue hormone, leptin, is involved in the pathogenesis of arterial hypertension. However, the mechanism of hypertensive effect of leptin is incompletely understood. We investigated whether antioxidant treatment could prevent leptin-induced hypertension. Hyperleptinemia was induced in male Wistar rats by administration of exogenous leptin (0.25 mg/kg twice daily s.c. for 7 days) and separate groups were simultaneously treated with superoxide scavenger, tempol, or NAD(P)H oxidase inhibitor, apocynin (2 mM in the drinking water). After 7 days, systolic blood pressure was 20.6% higher in leptin-treated than in control animals. Both tempol and apocynin prevented leptin-induced increase in blood pressure. Plasma concentration and urinary excretion of 8-isoprostanes increased in leptin-treated rats by 66.9% and 67.7%, respectively. The level of lipid peroxidation products, malonyldialdehyde + 4-hydroxyalkenals (MDA+4-HNE), was 60.3% higher in the renal cortex and 48.1% higher in the renal medulla of leptin-treated animals. Aconitase activity decreased in these regions of the kidney following leptin administration by 44.8% and 45.1%, respectively. Leptin increased nitrotyrosine concentration in plasma and renal tissue. Urinary excretion of nitric oxide metabolites (NO(x)) was 57.4% lower and cyclic GMP excretion was 32.0% lower in leptin-treated than in control group. Leptin decreased absolute and fractional sodium excretion by 44.5% and 44.7%, respectively. Co-treatment with either tempol or apocynin normalized 8-isoprostanes, MDA+4-HNE, aconitase activity, nitrotyrosine, as well as urinary excretion of NO(x), cGMP and sodium in rats receiving leptin. These results indicate that oxidative stress-induced NO deficiency is involved in the pathogenesis of leptin-induced hypertension.

Targeted intestinal overexpression of the immediate early gene tis7 in transgenic mice increases triglyceride absorption and adiposity

Following loss of functional small bowel surface area due to surgical resection, the remnant gut undergoes an adaptive response characterized by increased crypt cell proliferation and enhanced villus height and crypt depth, resulting in augmented intestinal nutrient absorptive capacity. Previous studies showed that expression of the immediate early gene tis7 is markedly up-regulated in intestinal enterocytes during the adaptive response. To study its role in the enterocyte, transgenic mice were generated that specifically overexpress TIS7 in the gut. Nucleotides -596 to +21 of the rat liver fatty acid-binding protein promoter were used to direct abundant overexpression of TIS7 into small intestinal upper crypt and villus enterocytes. TIS7 transgenic mice had increased total body adiposity and decreased lean muscle mass compared with normal littermates. Oxygen consumption levels, body weight, surface area, and small bowel weight were decreased. On a high fat diet, transgenic mice exhibited a more rapid and proportionately greater gain in body weight with persistently elevated total body adiposity and increased hepatic fat accumulation. Bolus fat feeding resulted in a greater increase in serum triglyceride levels and an accelerated appearance of enterocytic, lamina propria, and hepatic fat. Changes in fat homeostasis were linked to increased expression of genes involved in enterocytic triglyceride metabolism and changes in growth with decreased insulin-like growth factor-1 expression. Thus, TIS7 overexpression in the intestine altered growth, metabolic rate, adiposity, and intestinal triglyceride absorption. These results suggest that TIS7 is a unique mediator of nutrient absorptive and metabolic adaptation following gut resection.

Hepatic triglyceride contents are genetically determined in mice: results of a strain survey

To assess whether genetic factor(s) determine liver triglyceride (TG) levels, a 10-mouse strain survey of liver TG contents was performed. Hepatic TG contents were highest in BALB/cByJ, medium in C57BL/6J, and lowest in SWR/J in both genders. Ninety and seventy-six percent of variance in hepatic TG in males and females, respectively, was due to strain (genetic) effects. To understand the physiological/biochemical basis for differences in hepatic TG among the three strains, studies were performed in males of the BALB/cByJ, C57BL/6J, and SWR/J strains. In vivo hepatic fatty acid (FA) synthesis rates and hepatic TG secretion rates ranked BALB/cByJ approximately C57BL/6J > SWR/J. Hepatic 1-(14)C-labeled palmitate oxidation rates and plasma beta-hydroxybutyrate concentrations ranked in reverse order: SWR/J > BALB/cByJ approximately C57BL/6J. After 14 h of fasting, plasma-free FA and hepatic TG contents rose most in BALB/cByJ and least in SWR/J. beta-Hydroxybutyrate concentrations rose least in BALB/cByJ and most in SWR/J. Adaptation to fasting was most effective in SWR/J and least in BALB/cByJ, perhaps because BALB/cByJ are known to be deficient in SCAD, a short-chain FA oxidizing enzyme. To assess the role of insulin action, glucose tolerance test (GTT) was performed. GTT-glucose levels ranked C57BL/6J > BALB/cByJ approximately SWR/J. Thus strain-dependent (genetic) factors play a major role in setting hepatic TG levels in mice. Processes such as FA production and hepatic export in VLDL on the one hand and FA oxidation on the other, explain some of the strain-related differences in hepatic TG contents. Additional factor(s) in the development of fatty liver in BALB/cByJ remain to be demonstrated.

"New" hepatic fat activates PPARalpha to maintain glucose, lipid, and cholesterol homeostasis

De novo lipogenesis is an energy-expensive process whose role in adult mammals is poorly understood. We generated mice with liver-specific inactivation of fatty-acid synthase (FAS), a key lipogenic enzyme. On a zero-fat diet, FASKOL (FAS knockout in liver) mice developed hypoglycemia and fatty liver, which were reversed with dietary fat. These phenotypes were also observed after prolonged fasting, similarly to fasted PPARalpha-deficiency mice. Hypoglycemia, fatty liver, and defects in expression of PPARalpha target genes in FASKOL mice were corrected with a PPARalpha agonist. On either zero-fat or chow diet, FASKOL mice had low serum and hepatic cholesterol levels with elevated SREBP-2, decreased HMG-CoA reductase expression, and decreased cholesterol biosynthesis; these were also corrected with a PPARalpha agonist. These results suggest that products of the FAS reaction regulate glucose, lipid, and cholesterol metabolism by serving as endogenous activators of distinct physiological pools of PPARalpha in adult liver.

Expression of uncoupling protein 1 in skeletal muscle decreases muscle energy efficiency and affects thermoregulation and substrate oxidation

Skeletal muscle uncoupling by ectopic expression of mitochondrial uncoupling protein 1 (UCP1) has been shown to result in a lean phenotype in mice characterized by increased energy expenditure (EE), resistance to diet-induced obesity, and improved glucose tolerance. Here, we investigated in detail the effect of ectopic UCP1 expression in skeletal muscle on thermoregulation and energy homeostasis in HSA-mUCP1 transgenic mice. Thermoneutrality was determined to be ∼30°C for both wild-type (WT) and transgenic mice. EE, body temperature (Tb), activity, and respiratory quotient (RQ) were then measured over 24 h at ambient temperatures (Ta) of 30, 22, and 5°C. HSA-mUCP1 transgenic mice showed increased activity-related EE and heat loss but similar basal metabolic rate compared with WT. Tbat resting periods was progressively decreased with declining Tain HSA-mUCP1 transgenic mice but not in WT. Compared with WT littermates, the transgenic HSA-mUCP1 mice displayed increased RQ levels during night time, indicative of increased overall glucose oxidation, and failed to decrease their RQ levels with declining Ta. Thus increased EE caused by skeletal muscle uncoupling is clearly due to a decreased muscle energy efficiency during activity combined with increased glucose oxidation and a compromised thermoregulation associated with increased overall heat loss. At Tas below thermoneutrality, this puts increasing energy demands on the animals, whereas at thermoneutrality most differences in energy metabolism are not apparent any more.

Holloszy J, Medeiros DM, Schmidt RE, Saffitz JE, Abel ED, Semenkovich CF, Kelly DP. PGC-1alpha deficiency causes multi-system energy metabolic derangements: muscle dysfunction, abnormal weight control and hepatic steatosis

The gene encoding the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was targeted in mice. PGC-1α null (PGC-1α^−/−) mice were viable. However, extensive phenotyping revealed multi-system abnormalities indicative of an abnormal energy metabolic phenotype. The postnatal growth of heart and slow-twitch skeletal muscle, organs with high mitochondrial energy demands, is blunted in PGC-1α^−/− mice. With age, the PGC-1α^−/− mice develop abnormally increased body fat, a phenotype that is more severe in females. Mitochondrial number and respiratory capacity is diminished in slow-twitch skeletal muscle of PGC-1α^−/− mice, leading to reduced muscle performance and exercise capacity. PGC-1α^−/− mice exhibit a modest diminution in cardiac function related largely to abnormal control of heart rate. The PGC-1α^−/− mice were unable to maintain core body temperature following exposure to cold, consistent with an altered thermogenic response. Following short-term starvation, PGC-1α^−/− mice develop hepatic steatosis due to a combination of reduced mitochondrial respiratory capacity and an increased expression of lipogenic genes. Surprisingly, PGC-1α^−/− mice were less susceptible to diet-induced insulin resistance than wild-type controls. Lastly, vacuolar lesions were detected in the central nervous system of PGC-1α^−/− mice. These results demonstrate that PGC-1α is necessary for appropriate adaptation to the metabolic and physiologic stressors of postnatal life.

Eliminating the activity of the gene PGC-1 α in mice reveals its role in post-natal metabolism and provides a link to obesity and some intriguing differences with another report of this knockout