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Coupling is the process that links bone resorption to bone formation in a temporally and spatially coordinated manner within the remodeling cycle. Several lines of evidence point to the critical roles of osteoclast-derived coupling factors in the regulation of osteoblast performance. Here, we used a fractionated secretomic approach and identified the axon-guidance molecule SLIT3 as a clastokine that stimulated osteoblast migration and proliferation by activating [beta]-catenin. SLIT3 also inhibited bone resorption by suppressing osteoclast differentiation in an autocrine manner. Mice deficient in Slit3 or its receptor, Robo1, exhibited osteopenic phenotypes due to a decrease in bone formation and increase in bone resorption. Mice lacking Slit3 specifically in osteoclasts had low bone mass, whereas mice with either neuron-specific Slit3 deletion or osteoblast-specific Slit3 deletion had normal bone mass, thereby indicating the importance of SLIT3 as a local determinant of bone metabolism. In postmenopausal women, higher circulating SLIT3 levels were associated with increased bone mass. Notably, injection of a truncated recombinant SLIT3 markedly rescued bone loss after an ovariectomy. Thus, these results indicate that SLIT3 plays an osteoprotective role by synchronously stimulating bone formation and inhibiting bone resorption, making it a potential therapeutic target for metabolic bone diseases., Introduction Bone is a highly dynamic tissue that constantly undergoes changes and regeneration throughout adult life through a process called remodeling. This consists of 3 consecutive phases: the initiation of [...]

Inflammation in response to excess low-density lipoproteins in the blood is an important driver of atherosclerosis development. Due to its ability to enhance ATP-binding cassette A1-dependent (ABCA1-dependent) reverse cholesterol transport (RCT), liver X receptor (LXR) is an attractive target for the treatment of atherosclerosis. However, LXR also upregulates the expression of sterol regulatory element-binding protein 1c (SREBP-1c), leading to increased hepatic triglyceride synthesis, an independent risk factor for atherosclerosis. Here, we developed a strategy to separate the favorable and unfavorable effects of LXR by exploiting the specificity of the coactivator thyroid hormone receptor-associated protein 80 (TRAP80). Using human hepatic cell lines, we determined that TRAP80 selectively promotes the transcription of SREBP-1c but not ABCA1. Adenovirus-mediated expression of shTRAP80 inhibited LXR-dependent SREBP-1c expression and RNA polymerase II recruitment to the LXR responsive element (LXRE) of SREBP-1c, but not to the LXRE of ABCA1. In murine models, liver-specific knockdown of TRAP80 ameliorated liver steatosis and hypertriglyceridemia induced by LXR activation and maintained RCT stimulation by the LXR ligand. Together, these data indicate that TRAP80 is a selective regulator of hepatic lipogenesis and is required for LXR-dependent SREBP-1c activation. Moreover, targeting the interaction between TRAP80 and LXR should facilitate the development of potential LXR agonists that effectively prevent atherosclerosis., Introduction Liver X receptor (LXR) is a member of the nuclear receptor super-family and acts as a cholesterol sensor to regulate the expression of several key proteins involved in lipid [...]

Nitric oxide (NO) stimulates mitochondrial biogenesis. We recently reported that adiponectin synthesis is regulated by mitochondrial function in adipocytes. This study was undertaken to test the hypothesis that endothelial NO synthase (eNOS) plays an important role in adiponectin synthesis by producing NO and enhancing mitochondrial function in adipocytes. We examined the effects of eNOS knock-down on adiponectin synthesis in 3T3-L1 adipocytes and also examined plasma adiponectin levels and the mitochondria in adipose tissue of eNOS knockout ([eNOS.sup.-/-]) mice with and without chronic administration of a NO donor. In cultured 3T3-L1 adipocytes, eNOS siRNA decreased rosiglitazone-induced adiponectin secretion, which was associated with decreases in mitochondrial proteins and biogenesis factors. Plasma adiponectin concentrations were reduced in adult [eNOS.sup.-/-] mice compared with age-matched wild-type mice. Mitochondrial contents in adipose tissue were reduced in [eNOS.sup.-/-] mice, and this was associated with decreased expression of mitochondrial biogenesis factors, increased levels of 8-hydroxyguanosine, a biomarker of oxidative stress, and morphological abnormalities in mitochondria. Rosiglitazone-induced increases in adiponectin expression and mitochondrial content were also reduced significantly in [eNOS.sup.-/-] mice. Chronic administration of a NO donor reversed mitochondrial abnormalities and increased adiponectin expression in adipose tissue of [eNOS.sup.-/-] mice. eNOS plays an important role in adiponectin synthesis in adipocytes by increasing mitochondrial biogenesis and enhancing mitochondrial function. endothelial nitric oxide synthase; mitochondrial biogenesis; oxidative stress; nitric oxide doi: 10.1152/ajpendo.00008.2010.

AMP-activated protein kinase (AMPK) plays an important role in regulating whole body energy homeostasis. Recently, it has been demonstrated that berberine (BBR) exerts antiobesity and antidiabetic effects in obese and diabetic rodent models through the activation of AMPK in peripheral tissues. Here we show that BBR improves lipid dysregulation and fatty liver in obese mice through central and peripheral actions. In obese db/db and ob/ob mice, BBR treatment reduced liver weight, hepatic and plasma triglyceride, and cholesterol contents. In the liver and muscle of db/db mice, BBR promoted AMPK activity and fatty acid oxidation and changed expression of genes involved in lipid metabolism. Additionally, intracerebroventricular administration of BBR decreased the level of malonyl-CoA and stimulated the expression of fatty acid oxidation genes in skeletal muscle. Together, these data suggest that BBR would improve fatty liver in obese subjects, which is probably mediated not only by peripheral AMPK activation but also by neural signaling from the central nervous system. fatty acid oxidation; hypothalamus; malonyl-coenzyme A; AMP-activated protein kinase

Activation of nuclear factor-[kappa]B (NF-[kappa]B) occurs by dissociation from I[kappa]B after serine or tyrosine phosphorylation of I[kappa]B[alpha], but the way of NF-[kappa]B activation by high glucose has not been defined. High glucose is known to activate NF-[kappa]B via protein kinase C and reactive oxygen species (ROS). In this study, we investigated how high glucose activates NF-[kappa]B for CC chemokine ligand 2 production in cultured human glomerular endothelial cells. High glucose increased nuclear translocation of p65 and also increased NF-[kappa]B DNA binding activity. High glucose-induced NF-[kappa]B activation occurred without degradation of I[kappa]B[alpha]. In agreement with this, there was no increase in serine phosphorylation of I[kappa]B[alpha], while tyrosine phosphorylation of I[kappa]B[alpha] was increased by high glucose. High glucose increased the generation of ROS, whereas both [alpha]-lipoic acid and N-acetylcysteine scavenged the ROS and decreased high glucose-induced tyrosine phosphorylation of I[kappa]B[alpha], nuclear translocation of p65, and NF-[kappa]B DNA binding activity. Protein kinase C pseudosubstrate inhibited high glucose-induced ROS production, tyrosine phosphorylation of I[kappa]B[alpha], and nuclear translocation of p65. Both BAY 61-3606, a specific inhibitor of Syk protein-tyrosine kinase, and small interfering RNA directed against Syk inhibited high glucose-induced tyrosine phosphorylation of I[kappa]B[alpha] as well as p65 nuclear translocation. High glucose increased tyrosine phosphorylation of Syk, while it was inhibited by [alpha]-lipoic acid and protein kinase C pseudosubstrate. In summary, high glucose-induced NF-[kappa]B activation occurred not by serine phosphorylation of I[kappa]B[alpha]. Our data suggest that ROS-mediated tyrosine phosphorylation of I[kappa]B[alpha] is the mechanism for high glucose-induced NF-[kappa]B activation, and Syk may play a role in tyrosine phosphorylation of I[kappa]B[alpha]. CC chemokine ligand 2; protein kinase C: reactive oxygen species

Both mitochondrial dysfunction and alterations in mitochondrial DNA (mtDNA) are implicated in type 2 diabetes mellitus and insulin resistance. Evidence also suggests that metabolism of S-adenosyl-L-methionine (SAM), the universal methyl donor for biological methylation, is associated with mitochondrial dysfunction and insulin resistance. We investigated the effect of SAM on mtDNA density and insulin sensitivity using the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of type 2 diabetes mellitus and insulin resistance. To determine the short-term effect on mtDNA density, SAM (15 mg * [kg.sup.-1] * [d.sup.-1]) was administered intraperitoneally for 7 d to 6 male, 57-wk-old OLETF rats and 6 Long-Evans Tokushima Otsuka (LETO) rats of the same age as a nondiabetic control. To determine the long-term effect, the same dose of SAM was administered daily to 5 male, 6-wk-old OLETF rats until the age of 25 wk; 7 control OLETF rats received vehicle and 7 LETO rats were untreated. Skeletal muscle mtDNA density was measured by either competitive or multiplex PCR and insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. SAM treatment for 1 wk increased skeletal muscle mtDNA density of both OLETF and LETO rats. The long-term SAM treatment significantly reduced body weight gain as well as increased skeletal muscle mtDNA density and whole body insulin sensitivity in OLETF rats compared with their vehicle-treated controls. Furthermore, in all 3 groups, skeletal muscle mtDNA density correlated with insulin sensitivity (r = 0.752, P < 0.001). In conclusion, SAM treatment increased mtDNA density in the skeletal muscle, improved whole body insulin sensitivity, and prevented body weight gain in OLETF rats.

AMP-activated protein kinase (AMPK) functions as a fuel sensor in the cell and is activated when cellular energy is depleted. Here we report that [alpha]-lipoic acid ([alpha]-LA), a cofactor of mitochondrial enzymes, decreases hypothalamic AMPK activity and causes profound weight loss in rodents by reducing food intake and enhancing energy expenditure. Activation of hypothalamic AMPK reverses the effects of [alpha]-LA on food intake and energy expenditure. Intracerebroventricular (i.c.v.) administration of glucose decreases hypothalamic AMPK activity, whereas inhibition of intracellular glucose utilization through the administration of 2-deoxyglucose increases hypothalamic AMPK activity and food intake. The 2-deoxyglucose-induced hyperphagia is reversed by inhibiting hypothalamic AMPK. Our findings indicate that hypothalamic AMPK is important in the central regulation of food intake and energy expenditure and that [alpha]-LA exerts anti-obesity effects by suppressing hypothalamic AMPK activity. NOTE:: In the version of this article initially published online, the name of an author was misspelled. The name of the twelfth author should be "Benoit Viollet". This error has been corrected for the HTML and print versions of the article, Author(s): Min-Seon Kim [1]; Joong-Yeol Park [1]; Cherl Namkoong [2]; Pil-Geum Jang [2]; Je-Won Ryu [2]; Hai-Sun Song [2]; Ji-Young Yun [2]; Il-Seong Namgoong [1]; Joohun Ha [3]; In-Sun Park [...]

Epidemiologic data suggest a strong association between low birth weight and increased risk of metabolic syndrome in adult life. However, the underlying mechanisms are largely unknown. To test the hypothesis that mitochondrial changes may serve as a link between poor nutrition in early life and insulin resistance in later life,we investigated the effect of protein malnutrition during gestation and lactation on mitochondria of the liver and skeletal muscle. Female offspring of Sprague-Dawley rats fed a low protein diet (casein, 80 g/kg) were randomly divided into two groups and weaned onto either the low protein diet or a control diet (casein, 180 g/kg). As a control group, offspring of rats fed the control diet were weaned onto the control diet. The rats in each group were randomly divided into four groups that were killed at 5, 10, 15 and 20 wk of age. Both mitochondrial DNA content and the expression of mitochondrial DNA-encoded genes in liver and muscle were measured. Mitochondrial transcription factor A and antioxidant enzyme activities were also determined. The mitochondrial DNA content of the liver and skeletal muscle were reduced in fetal and early postnatal malnourished rats even when proper nutrition was supplied after weaning. These changes were accompanied by a decrease in mitochondrial DNA-encoded gene expression; however, they were not dependent on mitochondrial transcriptional factor A. Our findings indicate that poor nutrition in early life causes long-lasting changes in mitochondria that may contribute to the development of insulin resistance in later life. J. Nutr. 133: 3085-3090, 2003. KEY WORDS: * fetal protein malnutrition * insulin resistance * mitochondrial DNA * mitochondrial transcription factors