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Estrogen has an important role to play in energy homeostasis in both men and mice. Lack of estrogen results in the development of a metabolic syndrome in humans and rodents, including excess adiposity, hepatic steatosis (in male but not female aromatase knockout (ArKO) mice) and insulin resistance. Estrogen replacement results in a prompt reversal of the energy imbalance symptoms associated with estrogen deficiency. A corollary to the perturbed energy balance observed in the ArKO mouse is the death by apoptosis of dopaminergic neurons in the hypothalamic arcuate nucleus of male ArKO mice, an area of the brain pivotal to the regulation of energy uptake, storage, and mobilisation. An extension of our work exploring the relationship between estrogen and adiposity has been to examine the role played by androgens in energy balance. We have demonstrated that an increased androgen to estrogen ratio can promote visceral fat accumulation in the rodent by inhibiting AMPK activation and stimulating lipogenesis. Therefore, understanding the regulation of energy homeostasis is becoming an increasingly fascinating challenge, as the number of contributors, their communications, and the complexity of their interactions, involved in the preservation of this equilibrium continues to increase. Models of aromatase deficiency, both naturally occurring and engineered, will continue to provide valuable insights into energy homeostasis.
J Steroid Biochem Mol Biol
PMID:Estrogen and adiposity--utilizing models of aromatase deficiency to explore the relationship. 1764 92

The nuclear receptors peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the metabolic syndrome. Here, we show that they are direct regulators of the family of pyruvate dehydrogenase kinase (PDK) genes, whose products act as metabolic homeostats in sensing hunger and satiety levels in key metabolic tissues by modulating the activity of the pyruvate dehydrogenase complex. Mis-regulation of this tightly controlled network may lead to hyperglycemia. In human embryonal kidney cells we found the mRNA expression of PDK2, PDK3 and PDK4 to be under direct primary control of PPAR ligands, and in normal mouse kidney tissue Pdk2 and Pdk4 are PPAR targets. Both, treatment of HEK cells with PPARbeta/delta-specific siRNA and the genetic disruption of the Pparbeta/delta gene in mouse fibroblasts resulted in reduced expression of Pdk genes and abolition of induction by PPARbeta/delta ligands. These findings suggest that PPARbeta/delta is a key regulator of PDK genes, in particular the PDK4/Pdk4 gene. In silico analysis of the human PDK genes revealed two candidate PPAR response elements in the PDK2 gene, five in the PDK3 gene and two in the PDK4 gene, but none in the PDK1 gene. For seven of these sites we could demonstrate both PPARbeta/delta ligand responsiveness in context of their chromatin region and simultaneous association of PPARbeta/delta with its functional partner proteins, such as retinoidXreceptor, co-activator and mediator proteins and phosphorylated RNA polymerase II. In conclusion, PDK2, PDK3 and PDK4 are primary PPARbeta/delta target genes in humans underlining the importance of the receptor in the control of metabolism.
J Mol Biol 2007 Sep 14
PMID:Three members of the human pyruvate dehydrogenase kinase gene family are direct targets of the peroxisome proliferator-activated receptor beta/delta. 1766 20

Saturated free fatty acid (FFA) is a major source of metabolic stress that activates the c-Jun NH(2)-terminal kinase (JNK). This FFA-stimulated JNK pathway is relevant to hallmarks of metabolic syndrome, including insulin resistance. Here we used gene ablation studies in mice to demonstrate a central role for mixed-lineage protein kinases (MLK) in this signaling pathway. Saturated FFA causes protein kinase C (PKC)-dependent activation of MLK3 that subsequently causes increased JNK activity by a mechanism that requires the MAP kinase kinases MKK4 and MKK7. Loss of PKC, MLK3, MKK4, or MKK7 expression prevents FFA-stimulated JNK activation. Together, these data establish a signaling pathway that mediates effects of metabolic stress on insulin resistance.
Mol Cell 2007 Aug 03
PMID:Metabolic stress signaling mediated by mixed-lineage kinases. 1767 97

Glucocorticoids are widely used in the treatment of inflammatory and other diseases. However, high-dose or chronic administration often triggers troublesome side effects such as metabolic syndrome and osteoporosis. We recently described that one glucocorticoid receptor gene produces eight translational glucocorticoid receptor isoforms that have distinct gene-regulatory abilities. We show here that specific, but not all, glucocorticoid receptor isoforms induced apoptosis in human osteosarcoma U-2 OS bone cells. Whole human genome microarray analysis revealed that the majority of the glucocorticoid target genes were selectively regulated by specific glucocorticoid receptor isoforms. Real-time PCR experiments confirmed that proapoptotic enzymes necessary for cell death, granzyme A and caspase-6, were induced by specific glucocorticoid receptor isoforms. Chromatin immunoprecipitation assays further suggested that glucocorticoid receptor isoform-dependent induction of proapoptotic genes was likely due to selective coregulator recruitment and chromatin modification. Interestingly, the capabilities to transrepress proinflammatory genes were similar among glucocorticoid receptor isoforms. Together, these findings provide new evidence that translational glucocorticoid receptor isoforms can elicit distinct glucocorticoid responses and may be useful for the development of safe glucocorticoids with reduced side effects.
Mol Cell Biol 2007 Oct
PMID:Selective regulation of bone cell apoptosis by translational isoforms of the glucocorticoid receptor. 1768 54

The metabolic syndrome is strongly associated with insulin resistance and consists of a constellation of factors such as hypertension and hyperlipidemia that raise the risk for cardiovascular diseases and diabetes mellitus. There is widespread agreement that the renin-angiotensin system (RAS) plays a pivotal role in the pathogenesis of insulin resistance and cardiovascular disease in diabetes. Indeed, large clinical trials have demonstrated substantial benefit of the blockade of this system for cardiovascular end-organ protection. Thus the blockade of the RAS may be a promising strategy for the treatment of the patients with the metabolic syndrome. Although several types of angiotensin II type 1 (AT(1)) receptor blockers (ARBs) are commercially available for the treatment of patients with hypertension, we have recently found that telmisartan (Micardis) could have the strongest binding affinity to AT(1) receptor. Further, telmisartan is reported to act as a partial agonist of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). These observations suggest that, due to its unique PPAR-gamma-modulating activity, telmisartan may be one of the most promising sartans for the treatment of cardiometabolic disorders. In this paper, we reviewed the potential utility of telmisartan in insulin resistance and vascular complications in diabetes.
Curr Mol Med 2007 Aug
PMID:Potential utility of telmisartan, an angiotensin II type 1 receptor blocker with peroxisome proliferator-activated receptor-gamma (PPAR-gamma)-modulating activity for the treatment of cardiometabolic disorders. 1769 61

Sarcopenia is related to metabolic syndrome in postmenopausal women. Hormone replacement therapies with androgens improve muscle functions by molecular mechanisms that are still unknown, at least partly because the skeletal muscle transcriptome has been less characterized in females. We performed the serial analysis of gene expression method in six experimental groups, intact (male and female), ovariectomy (OVX), OVX+dihydrotestosterone (DHT) injection 1, 3, or 24 h before kill in mice. The 438 transcript species differentially expressed between gender showed that females had higher expression levels of mRNA related to cytoskeleton/contractile apparatus and mitochondrial processes as well as protein, lipid, and amino acid metabolisms. In females, OVX and DHT modulated 109 and 128 transcript species respectively. OVX repressed transcripts of fast/glycolytic fiber, glycolysis, and glucose transport, whereas all these effects were reversed 3 h after the DHT injection. Moreover, DHT treatment induced transcripts which reduce intracellular Ca(2+) level at early time points. These results may suggest that DHT treatment in OVX mice increases muscle contractility by affecting fiber distribution and intracellular Ca(2+) concentration as well as improving glucose metabolism. On the other hand, transcripts of fast/oxidative fiber, oxidative phosphorylation, and ATP production were repressed 24 h after DHT administration. In our previous study using male mice, transcripts in oxidative phosphorylation and ATP production were induced 24 h after DHT injection (Yoshioka M, Boivin A, Ye P, Labrie F & St-Amand J 2006 Effects of dihydrotestosterone on skeletal muscle transcriptome in mice measured by serial analysis of gene expression. Journal of Molecular Endocrinology 36 247-259 ). These results demonstrate gender differences in DHT actions on skeletal muscle, and contribute to a precise understanding of the molecular mechanisms of androgen actions in the female skeletal muscle.
J Mol Endocrinol 2007 Aug
PMID:Gender difference of androgen actions on skeletal muscle transcriptome. 1769 11

Certain selective serotonin reuptake inhibitors (SSRIs) induce the clinical and biochemical manifestations of a metabolic syndrome by as yet unknown mechanism. Here we demonstrate that incubation (1 h) of rat hepatoma Fao cells with the SSRIs paroxetine and sertraline, but not with the atypical antipsychotic drug olanzapine, inhibited the insulin-stimulated Tyr phosphorylation of the insulin receptor substrate-1 (IRS-1) with half-maximal effects at approximately 10 microM. This inhibition correlated with a rapid phosphorylation and activation of a number of Ser/Thr IRS-1 kinases including JNK, S6K1, ERK and p38 MAPK, but not PKB (Akt). JNK appears as a key player activated by SSRIs because specific JNK inhibitors partially eliminated the effects of these drugs. The SSRIs induced the phosphorylation of IRS-1 on S307 and S408, which inhibits IRS-1 function and insulin signaling. These results implicate selected SSRIs as inhibitors of insulin signaling and as potential inducers of cellular insulin resistance.
Mol Cell Neurosci 2007 Nov
PMID:Antidepressants induce cellular insulin resistance by activation of IRS-1 kinases. 1772 40

There is increasing acknowledgment of the public health burden of metabolic syndrome. The metabolic syndrome is defined as emerging cardiovascular risk factors, or atherosclerosis, that are related to underlying insulin resistance. One of the adipokines, adiponectin, has antiatherogenic effects and augments the metabolic effects of insulin. To reduce mortality from cardiovascular disease, it is important to understand the pathophysiological properties of adiponectin and receptors in atherosclerotic regions. Recently, T-cadherin, which has been recognized as a unique cadherin molecule, has been characterized as a novel adiponectin receptor on vascular endothelial cells and smooth muscle. Notably, T-cadherin (also known as CDH13, cadherin 13, and H-cadherin) is abundantly expressed in injured vascular endothelial and smooth muscle cells in atherosclerotic regions. In the present review, we describe recent progress in research on adiponectin receptors, with emphasis on the unique vascular adiponectin receptor, T-cadherin, and its role in vascular disease.
Med Mol Morphol 2007 Sep
PMID:Adiponectin receptors, with special focus on the role of the third receptor, T-cadherin, in vascular disease. 1787 43

Lipid homeostasis requires a strict balance between lipid intake and consumption. This balance is controlled by different systems that regulate food intake, energy storage and energy expenditure. This review focuses on the roles of peroxisome proliferator- activated receptors (PPARs) in some of these regulatory processes. PPARs are transcription factors that bind and are activated by fatty acids and fatty acid derivatives. They act as lipid sensors and adapt the metabolism and development of various tissues to lipid availability. Due to their actions on lipid metabolism, PPARs are bona fide therapeutic targets in the treatment of metabolic syndrome not only by affecting gene expression patterns in several tissues but also by inducing remodeling of tissues such as adipose or skeletal muscle.
Cell Mol Life Sci 2007 Oct
PMID:Peroxisome proliferator-activated receptors as sensors of fatty acids and derivatives. 1787 21

The metabolic syndrome (also referred to as syndrome X or the insulin resistance syndrome) has emerged as an important cluster of risk factors for atherosclerotic disease. Patients with the syndrome also are at increased risk for developing type 2 diabetes mellitus. Common features are central (abdominal) obesity, insulin resistance, hypertension, and dyslipidemia. Weight reduction deserves first priority in individuals with abdominal obesity and the metabolic syndrome. Both weight reduction and maintenance of a lower weight are best achieved by a combination of reduced caloric intake and increased physical activity. Dietary patterns close to the Mediterranean diet and rich in fruit and vegetables, and high in monounsaturated fats are negatively associated with features of the metabolic syndrome. Some recent studies dealing specifically with the effect of interventions on the resolution of the metabolic syndrome have demonstrated a 25% net reduction in the prevalence of the syndrome following lifestyle changes mainly based on nutritional recommendations. Similar rates of resolution have been obtained with drugs, such as rosiglitazone and rimonabant. The favourable benefit/hazard ratio makes Mediterranean-style diets particularly promising to reduce the cardiovascular burden associated with the metabolic syndrome.
Mol Nutr Food Res 2007 Oct
PMID:Mediterranean diet and the metabolic syndrome. 1787 92


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