Dual orexin receptor antagonist drug suvorexant can help in amelioration of predictable chronic mild stress-induced hyperalgesia

AIMS

This study aimed to evaluate the involvement of the orexin system in predictable chronic mild stress (PCMS) and the effects of suvorexant, a dual orexin receptor antagonist, on nociceptive behavior in PCMS.

MATERIALS AND METHODS

Male C57BL/6 J mice were separated into various PCMS groups: a control group with sawdust on the floor of the rearing cage (C), a group with mesh wire on the floor (M), and a group with water just below the mesh wire (W). Activation of lateral hypothalamic orexin neurons was assessed using immunofluorescence. In another experiment, half of the mice in each group were administered an intraperitoneal injection of suvorexant (10 mg/kg), and the remaining mice were injected with the same amount of vehicle (normal saline). Thermal hyperalgesia was examined using tail immersion and hot plate tests, while mechanical hyperalgesia was investigated using the tail pinch test after 21 days of PCMS.

KEY FINDINGS

Animals subjected to PCMS showed an increased percentage of activated orexin neurons in the lateral hypothalamic region after 21 days. Mice raised in the PCMS environment showed increased pain sensitivity in several pain tests; however, the symptoms were significantly reduced by suvorexant administration.

SIGNIFICANCE

The findings revealed that PCMS activates hypothalamic orexin neuronal activity, and the use of suvorexant can help attenuate PCMS-induced thermal and mechanical hyperalgesia.

Short-term physical inactivity induces diacylglycerol accumulation and insulin resistance in muscle via lipin1 activation

Physical inactivity impairs muscle insulin sensitivity. However, its mechanism is unclear. To model physical inactivity, we applied 24-h hind-limb cast immobilization (HCI) to mice with normal or high-fat diet (HFD) and evaluated intramyocellular lipids and the insulin signaling pathway in the soleus muscle. Although 2-wk HFD alone did not alter intramyocellular diacylglycerol (IMDG) accumulation, HCI alone increased it by 1.9-fold and HCI after HFD further increased it by 3.3-fold. Parallel to this, we found increased protein kinase C ε (PKCε) activity, reduced insulin-induced 2-deoxyglucose (2-DOG) uptake, and reduced phosphorylation of insulin receptor β (IRβ) and Akt, key molecules for insulin signaling pathway. Lipin1, which converts phosphatidic acid to diacylglycerol, showed increase of its activity by HCI, and dominant-negative lipin1 expression in muscle prevented HCI-induced IMDG accumulation and impaired insulin-induced 2-DOG uptake. Furthermore, 24-h leg cast immobilization in human increased lipin1 expression. Thus, even short-term immobilization increases IMDG and impairs insulin sensitivity in muscle via enhanced lipin1 activity.NEW & NOTEWORTHY Physical inactivity impairs muscle insulin sensitivity. However, its mechanism is unclear. To model physical inactivity, we applied 24-h hind-limb cast immobilization to mice with normal or high-fat diet and evaluated intramyocellular lipids and the insulin signaling pathway in the soleus muscle. We found that even short-term immobilization increases intramyocellular diacylglycerol and impairs insulin sensitivity in muscle via enhanced lipin1 activity.

Intracranial mast cells contribute to the control of social behavior in male mice

Mast cells (MCs) exist intracranially and have been reported to affect higher brain functions in rodents. However, the role of MCs in the regulation of emotionality and social behavior is unclear. In the present study, using male mice, we examined the relationship between MCs and social behavior and investigated the underlying mechanisms. Wild-type male mice intraventricularly injected with a degranulator of MCs exhibited a marked increase in a three-chamber sociability test. In addition, removal of MCs in Mast cell-specific Toxin Receptor-mediated Conditional cell Knock out (Mas-TRECK) male mice showed reduced social preference levels in a three-chamber sociability test without other behavioral changes, such as anxiety-like and depression-like behavior. Mas-TRECK male mice also had reduced serotonin content and serotonin receptor expression and increased oxytocin receptor expression in the brain. These results suggested that MCs may contribute to the regulation of social behavior in male mice. This effect may be partially mediated by serotonin derived from MCs in the brain.

Deletion of H-ferritin in macrophages alleviates obesity and diabetes induced by high-fat diet in mice

AIMS/HYPOTHESIS

Iron accumulation affects obesity and diabetes, both of which are ameliorated by iron reduction. Ferritin, an iron-storage protein, plays a crucial role in iron metabolism. H-ferritin exerts its cytoprotective action by reducing toxicity via its ferroxidase activity. We investigated the role of macrophage H-ferritin in obesity and diabetes.

METHODS

Conditional macrophage-specific H-ferritin (Fth, also known as Fth1) knockout (LysM-Cre Fth KO) mice were used and divided into four groups: wild-type (WT) and LysM-Cre Fth KO mice with normal diet (ND), and WT and LysM-Cre Fth KO mice with high-fat diet (HFD). These mice were analysed for characteristics of obesity and diabetes, tissue iron content, inflammation, oxidative stress, insulin sensitivity and metabolic measurements. RAW264.7 macrophage cells were used for in vitro experiments.

RESULTS

Iron concentration reduced, and mRNA expression of ferroportin increased, in macrophages from LysM-Cre Fth KO mice. HFD-induced obesity was lower in LysM-Cre Fth KO mice than in WT mice at 12 weeks (body weight: KO 34.6 ± 5.6 g vs WT 40.1 ± 5.2 g). mRNA expression of inflammatory cytokines and infiltrated macrophages and oxidative stress increased in the adipose tissue of HFD-fed WT mice, but was not elevated in HFD-fed LysM-Cre Fth KO mice. However, WT mice fed an HFD had elevated iron concentration in adipose tissue and spleen, which was not observed in LysM-Cre Fth KO mice fed an HFD (adipose tissue [μmol Fe/g protein]: KO 1496 ± 479 vs WT 2316 ± 866; spleen [μmol Fe/g protein]: KO 218 ± 54 vs WT 334 ± 83). Moreover, HFD administration impaired both glucose tolerance and insulin sensitivity in WT mice, which was ameliorated in LysM-Cre Fth KO mice. In addition, energy expenditure, mRNA expression of thermogenic genes, and body temperature were higher in KO mice with HFD than WT mice with HFD. In vitro experiments showed that iron content was reduced, and lipopolysaccharide-induced Tnf-α (also known as Tnf) mRNA upregulation was inhibited in a macrophage cell line transfected with Fth siRNA.

CONCLUSIONS/INTERPRETATION

Deletion of macrophage H-ferritin suppresses the inflammatory response by reducing intracellular iron levels, resulting in the prevention of HFD-induced obesity and diabetes. The findings from this study highlight macrophage iron levels as a potential therapeutic target for obesity and diabetes.

Dopamine stimulation of the septum enhances exercise efficiency during complicated treadmill running in mice

We aimed to identify the neurotransmitters and brain regions involved in exercise efficiency in mice during continuous complicated exercises. Male C57BL/6J mice practiced treadmill running with intermittent obstacles on a treadmill for 8 days. Oxygen uptake (VO2) during treadmill running was measured as exercise efficiency. After obstacle exercise training, the VO2 measured during treadmill running with obstacles decreased significantly. Obstacle exercise-induced c-Fos expressions and dopamine turnover (DOPAC/dopamine) in the septum after obstacle exercise training were significantly higher than that before training. The dopamine turnover was correlated with exercise efficiency on the 3rd day after exercise training. Furthermore, the training effect on exercise efficiency was significantly decreased by injection of dopamine receptor antagonists into the septum and was associated with decreased c-Fos expressions in the septum and hippocampus of the mice. These results suggest that dopaminergic function in the septum is involved in exercise efficiency during continuous complicated exercises.

Activation of AMPK-Regulated CRH Neurons in the PVH is Sufficient and Necessary to Induce Dietary Preference for Carbohydrate over Fat

Food selection is essential for metabolic homeostasis and is influenced by nutritional state, food palatability, and social factors such as stress. However, the mechanism responsible for selection between a high-carbohydrate diet (HCD) and a high-fat diet (HFD) remains unknown. Here, we show that activation of a subset of corticotropin-releasing hormone (CRH)-positive neurons in the rostral region of the paraventricular hypothalamus (PVH) induces selection of an HCD over an HFD in mice during refeeding after fasting, resulting in a rapid recovery from the change in ketone metabolism. These neurons manifest activation of AMP-activated protein kinase (AMPK) during food deprivation, and this activation is necessary and sufficient for selection of an HCD over an HFD. Furthermore, this effect is mediated by carnitine palmitoyltransferase 1c (CPT1c). Thus, our results identify the specific neurons and intracellular signaling pathway responsible for regulation of the complex behavior of selection between an HCD and an HFD. VIDEO ABSTRACT.

Role of orexin in exercise-induced leptin sensitivity in the mediobasal hypothalamus of mice

Orexin is known as an important neuropeptide in the regulation of energy metabolism. However, the role of orexin in exercise-induced leptin sensitivity in the hypothalamus has been unclear. In this study, we determined the effect of transient treadmill exercise on leptin sensitivity in the mediobasal hypothalamus (MBH) of mice and examined the role of orexin in post-exercise leptin sensitivity. Treadmill running for 45 min increased the orexin neuron activity in mice. Intraperitoneal injection of a submaximal dose of leptin after exercise stimulated the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in MBH of mice post-exercise compared with that in non-exercised mice, although intracerebroventricular (icv) injection of leptin did not enhance STAT3 phosphorylation, even after exercise. Icv injection of an orexin receptor antagonist, SB334867 reduced STAT3 phosphorylation, which was enhanced by icv injection of orexin but not by direct injection of orexin into MBH. Exercise increased the phosphorylation of extracellular signal-regulated kinases (ERKs) in the MBH of mice, while ERK phosphorylation was reduced by SB334867. Leptin injection after exercise increased the leptin level in MBH, whereas icv injection of SB334867 suppressed the increase in the leptin level in MBH of mice. These results indicate that the activation of orexin neurons by exercise may contribute to the enhancement of leptin sensitivity in MBH. This effect may be mediated by increased transportation of circulating leptin into MBH, with the involvement of ERK phosphorylation.

Sufficient intake of high-fat food attenuates stress-induced social avoidance behavior

AIMS

Psychosocial stress is a form of mental stress associated with human relationships that underlies the pathogenesis of mental disorders such as depression. Previous studies have suggested that intake of energy-dense foods, also known as "palatable foods," can relieve psychosocial stress. However, it remains unclear whether the volume of palatable food affects abnormal behavior induced by psychosocial stress. In the present study, we aimed to determine whether levels of high-fat food intake significantly influence psychosocial stress using the social-defeat stress (SDS) paradigm.

MAIN METHODS

Mice subjected to SDS ate either a high-fat or normal chow diet for 10 days. Behavioral tests were conducted following the completion of the SDS paradigm. The hypothalamus, liver, and blood were examined post-mortem.

KEY FINDINGS

Mice with sufficient intake of high-fat chow immediately following exposure to SDS did not exhibit social avoidance behavior, suggesting that a high-fat diet may improve social behavior. However, inadequate intake of high-fat food, which did not alter cholesterol metabolism or hypothalamic-pituitary-adrenal axis activity, was not associated with such benefits, instead increased anxiety-like behavior.

SIGNIFICANCE

The results of the present study demonstrate that eating a high-fat diet may attenuate stress, but that this benefit disappears with insufficient intake of high-fat foods. The benefits of a high-fat diet under SDS may be related to cholesterol metabolism in the liver.

Enhancement of fear learning in PPARα knockout mice

Peroxisome proliferator-activated receptor alpha (PPARα) is a member of the nuclear receptor superfamily and regulates fatty acid oxidation. Although PPARα is expressed not only in the peripheral tissues but also in the brain, its role in higher brain function is unclear. In this study, we investigated the role of PPARα in the control of behavior, including memory/learning and mood change, using PPARα knockout (KO) mice. A significant difference between wild-type (WT) and KO mice was seen in the passive avoidance test, demonstrating that KO mice showed enhanced fear leaning. In the amygdala of KO mice, the levels of dopamine and its metabolites were increased, and the mRNA expression of dopamine degrading enzyme was decreased. When dopamine D1 receptor antagonist was administered, the enhanced fear learning observed in KO mice was attenuated. These results suggest that PPARα is involved in the regulation of emotional memory via the dopamine pathway in the amygdala.

Intracerebroventricular injection of ghrelin decreases wheel running activity in rats

There is an increasing interest in elucidating the molecular mechanisms by which voluntary exercise is regulated. In this study, we examined how the central nervous system regulates exercise. We used SPORTS rats, which were established in our laboratory as a highly voluntary murine exercise model. SPORTS rats showed lower levels of serum ghrelin compared with those of the parental line of Wistar rats. Intracerebroventricular and intraperitoneal injection of ghrelin decreased wheel-running activity in SPORTS rats. In addition, daily injection of the ghrelin inhibitor JMV3002 into the lateral ventricles of Wistar rats increased wheel-running activity. Co-administration of obestatin inhibited ghrelin-induced increases in food intake but did not inhibit ghrelin-induced suppression of voluntary exercise in rats. Growth hormone secretagogue receptor (GHSR) in the hypothalamus and hippocampus of SPORTS rats was not difference that in control rats. We created an arcuate nucleus destruction model by administering monosodium glutamate (MSG) to neonatal SPORTS rats. Injection of ghrelin into MSG-treated rats decreased voluntary exercise but did not increase food intake, suggesting that wheel-running activity is not controlled by the arcuate nucleus neurons that regulate feeding. These results provide new insights into the mechanism by which ghrelin regulates voluntary activity independent of arcuate nucleus neurons.

Sympathetic Nerve Activity Maintains an Anti-Inflammatory State in Adipose Tissue in Male Mice by Inhibiting TNF-α Gene Expression in Macrophages

Adipose tissue macrophages (ATMs) play an important role in the inflammatory response in obese animals. How ATMs are regulated in lean animals has remained elusive, however. We now show that the sympathetic nervous system (SNS) is necessary to maintain the abundance of the mRNA for the proinflammatory cytokine TNF-α at a low level in ATMs of lean mice. Intracerebroventricular injection of agouti-related neuropeptide increased the amount of TNF-α mRNA in epididymal (epi) white adipose tissue (WAT), but not in interscapular brown adipose tissue (BAT), through inhibition of sympathetic nerve activity in epiWAT. The surgical denervation and β-adrenergic antagonist propranolol up-regulated TNF-α mRNA in both epiWAT and BAT in vivo. Signaling by the β2-adrenergic receptor (AR) and protein kinase A down-regulated TNF-α mRNA in epiWAT explants and suppressed lipopolysaccharide-induced up-regulation of TNF-α mRNA in the stromal vascular fraction of this tissue. β-AR-deficient (β-less) mice manifested an increased plasma TNF-α concentration and increased TNF-α mRNA abundance in epiWAT and BAT. TNF-α mRNA abundance was greater in ATMs (CD11b(+) cells of the stromal vascular fraction) from epiWAT or BAT of wild-type mice than in corresponding CD11b(-) cells, and β2-AR mRNA abundance was greater in ATMs than in CD11b(-) cells of epiWAT. Our results show that the SNS and β2-AR-protein kinase A pathway maintain an anti-inflammatory state in ATMs of lean mice in vivo, and that the brain melanocortin pathway plays a role in maintaining this state in WAT of lean mice via the SNS.

Ketone body metabolism and sleep homeostasis in mice

A link has been established between energy metabolism and sleep homeostasis. The ketone bodies acetoacetate and β-hydroxybutyrate, generated from the breakdown of fatty acids, are major metabolic fuels for the brain under conditions of low glucose availability. Ketogenesis is modulated by the activity of peroxisome proliferator-activated receptor alpha (PPARα), and treatment with a PPAR activator has been shown to induce a marked increase in plasma acetoacetate and decreased β-hydroxybutyrate in mice, accompanied by increased slow-wave activity during non-rapid eye movement (NREM) sleep. The present study investigated the role of ketone bodies in sleep regulation. Six-hour sleep deprivation increased plasma ketone bodies and their ratio (acetoacetate/β-hydroxybutyrate) in 10-week-old male mice. Moreover, sleep deprivation increased mRNA expression of ketogenic genes such as PPARα and 3-hydroxy-3-methylglutarate-CoA synthase 2 in the brain and decreased ketolytic enzymes such as succinyl-CoA: 3-oxoacid CoA transferase. In addition, central injection of acetoacetate, but not β-hydroxybutyrate, markedly increased slow-wave activity during NREM sleep and suppressed glutamate release. Central metabolism of ketone bodies, especially acetoacetate, appears to play a role in the regulation of sleep homeostasis.

Extracellular signal-regulated kinase in the ventromedial hypothalamus mediates leptin-induced glucose uptake in red-type skeletal muscle

Leptin is a key regulator of glucose metabolism in mammals, but the mechanisms of its action have remained elusive. We now show that signaling by extracellular signal-regulated kinase (ERK) and its upstream kinase MEK in the ventromedial hypothalamus (VMH) mediates the leptin-induced increase in glucose utilization as well as its insulin sensitivity in the whole body and in red-type skeletal muscle of mice through activation of the melanocortin receptor (MCR) in the VMH. In contrast, activation of signal transducer and activator of transcription 3 (STAT3), but not the MEK-ERK pathway, in the VMH by leptin enhances the insulin-induced suppression of endogenous glucose production in an MCR-independent manner, with this effect of leptin occurring only in the presence of an increased plasma concentration of insulin. Given that leptin requires 6 h to increase muscle glucose uptake, the transient activation of the MEK-ERK pathway in the VMH by leptin may play a role in the induction of synaptic plasticity in the VMH, resulting in the enhancement of MCR signaling in the nucleus and leading to an increase in insulin sensitivity in red-type muscle.

Maternal dietary restriction alters offspring's sleep homeostasis

Nutritional state in the gestation period influences fetal growth and development. We hypothesized that undernutrition during gestation would affect offspring sleep architecture and/or homeostasis. Pregnant female mice were assigned to either control (fed ad libitum; AD) or 50% dietary restriction (DR) groups from gestation day 12 to parturition. After parturition, dams were fed AD chow. After weaning, the pups were also fed AD into adulthood. At adulthood (aged 8-9 weeks), we carried out sleep recordings. Although offspring mice displayed a significantly reduced body weight at birth, their weights recovered three days after birth. Enhancement of electroencephalogram (EEG) slow wave activity (SWA) during non-rapid eye movement (NREM) sleep was observed in the DR mice over a 24-hour period without changing the diurnal pattern or amounts of wake, NREM, or rapid eye movement (REM) sleep. In addition, DR mice also displayed an enhancement of EEG-SWA rebound after a 6-hour sleep deprivation and a higher threshold for waking in the face of external stimuli. DR adult offspring mice exhibited small but significant increases in the expression of hypothalamic peroxisome proliferator-activated receptor α (Pparα) and brain-specific carnitine palmitoyltransferase 1 (Cpt1c) mRNA, two genes involved in lipid metabolism. Undernutrition during pregnancy may influence sleep homeostasis, with offspring exhibiting greater sleep pressure.

Intestinal fatty acid infusion modulates food preference as well as calorie intake via the vagal nerve and midbrain-hypothalamic neural pathways in rats

The intestine plays important roles in the regulation of feeding behavior by sensing macronutrients. Intestinal fatty acids strongly suppress food intake, but little is known about whether intestinal fatty acids affect food preference. We investigated the effects of jejunal fatty acids infusion on food preference by conducting two-diet choice experiments in rats fed a high-fat diet (HFD) and a high-carbohydrate diet (HCD). Jejunal linoleic acid (18:2) infusion reduced HFD intake dose-dependently, while HCD intake increased with the middle dose of the infusion we examined (100 μL/h) and reduced to the control level with the higher doses (150 and 200 μL/h). α-Linolenic acid (18:3), but not caprylic acid (8:0), altered the food preference and total calorie intake in the same manner as linoleic acid. Linoleic acid infusion dose-dependently increased plasma glucagon-like peptide-1, peptide YY and cholecystokinin levels, but not ghrelin levels. Subdiaphragmatic vagotomy or midbrain transection prevented the change in food preference and total calorie intake by linoleic acid infusion. Jejunal linoleic acid infusion increased norepinephrine turnover in the paraventricular hypothalamic nucleus, while intracerebroventricular injection of idazoxan, an α2-adrenergic receptor (AR) antagonist, suppressed the increased HCD intake, but did not affect the decreased HFD intake. These findings indicated that intestinal long-chain fatty acids modulated food preference as well as total calorie intake via the vagal nerve and midbrain-hypothalamic neural pathways. The effects of the α2-AR antagonist in the brain suggested that the brain distinctly controlled HCD and HFD intake in response to jejunal linoleic acid infusion.

An enzymatic photometric assay for 2-deoxyglucose uptake in insulin-responsive tissues and 3T3-L1 adipocytes

An enzymatic assay adapted to photometric analysis with 96-well microplates was evaluated for the measurement of 2-deoxyglucose (2DG) uptake in insulin-responsive tissues and differentiated 3T3-L1 adipocytes. For in vivo measurements, a small amount of nonradiolabeled 2DG was injected into mice without affecting glucose metabolism. For photometric quantification of the small amount of 2-deoxyglucose 6-phosphate (2DG6P) that accumulates in cells, we introduced glucose-6-phosphate dehydrogenase, glutathione reductase, and 5,5'-dithiobis(2-nitrobenzoic acid) to the recycling amplification reaction of NADPH. We optimized the enzyme reaction for complete oxidation of endogenous glucose 6-phosphate (G6P) and glucose in mouse tissues in vivo and serum as well as in 3T3-L1 adipocytes in vitro. All reactions are performed in one 96-well microplate by consecutive addition of reagents, and the assay is able to quantify 2DG and 2DG6P in the range of 5-80 pmol. The results obtained with the assay for 2DG uptake in vitro and in vivo in the absence or presence of insulin stimulation was similar to those obtained with the standard radioisotopic method. Thus, the enzymatic assay should prove to be useful for measurement of 2DG uptake in insulin-responsive tissues in vivo as well as in cultured cells.

Lack of TRPM2 impaired insulin secretion and glucose metabolisms in mice

OBJECTIVE

TRPM2 is a Ca²(+)-permeable nonselective cation channel activated by adenosine dinucleotides. We previously demonstrated that TRPM2 is activated by coapplication of heat and intracellular cyclic adenosine 5'-diphosphoribose, which has been suggested to be involved in intracellular Ca²(+) increase in immunocytes and pancreatic β-cells. To clarify the involvement of TRPM2 in insulin secretion, we analyzed TRPM2 knockout (TRPM2-KO) mice.

RESEARCH DESIGN AND METHODS

Oral and intraperitoneal glucose tolerance tests (OGTT and IPGTT) were performed in TRPM2-KO and wild-type mice. We also measured cytosolic free Ca²(+) in single pancreatic cells using fura-2 microfluorometry and insulin secretion from pancreatic islets.

RESULTS

Basal blood glucose levels were higher in TRPM2-KO mice than in wild-type mice without any difference in plasma insulin levels. The OGTT and IPGTT demonstrated that blood glucose levels in TRPM2-KO mice were higher than those in wild-type mice, which was associated with an impairment in insulin secretion. In isolated β-cells, smaller intracellular Ca²(+) increase was observed in response to high concentrations of glucose and incretin hormone in TRPM2-KO cells than in wild-type cells. Moreover, insulin secretion from the islets of TRPM2-KO mice in response to glucose and incretin hormone treatment was impaired, whereas the response to tolbutamide, an ATP-sensitive potassium channel inhibitor, was not different between the two groups.

CONCLUSIONS

These results indicate that TRPM2 is involved in insulin secretion stimulated by glucose and that further potentiated by incretins. Thus, TRPM2 may be a new target for diabetes therapy.

Induction of hypothalamic Sirt1 leads to cessation of feeding via agouti-related peptide

Silent information regulator (SIR)2 is an nicotinamide adenine dinucleotide dependent deacetylase implicated in the regulation of life span in species as diverse as yeast, worms, and flies. Mammalian Sirt1 is the most closely related homolog of the SIR2 gene. Pharmacological activators of Sirt1 have been reported to increase the life span and improve the health of mice fed a high-fat diet and to reverse diabetes in rodents. Sirt1 links the energy availability status with cellular metabolism in peripheral organs including liver, pancreas, muscle, and white adipose tissue. Insulin and leptin signaling regulate food intake by controlling the expression of orexigenic and anorexigenic neuropeptides in the arcuate nucleus of the hypothalamus via Forkhead box O (Foxo)-1 and signal transducer and activator of transcription-3. Sirt1 has been reported to improve insulin sensitivity in vitro, but the role of hypothalamic Sirt1 in regulating feeding has not been addressed. We found that hypothalamic Sirt1 protein levels increase on feeding, and this induction is abrogated in diet-induced obese mice and db/db mice. We also demonstrate for the first time that Sirt1 protein turnover is regulated by the proteasome and ubiquitination in a hypothalamic cell line and in vivo by feeding, and this regulation is not seen in a pituitary cell line AtT20. Forced expression of wild-type Sirt1 in the mediobasal hypothalamus by adenovirus microinjection suppressed Foxo1-induced hyperphagia, a model for central insulin resistance. Moreover, Sirt1 suppressed Foxo1-dependent expression of the orexigenic neuropeptide Agouti-related peptide in vitro. We propose that on feeding, Sirt1 protein is stabilized in the hypothalamus, leading to decreased Foxo1-dependent expression of orexigenic neuropeptide Agouti-related peptide and cessation of feeding.

Metabolic adaptation of mice in a cool environment

Homeothermic animals, including humans, live by adapting to changes in ambient temperature. Numerous studies have demonstrated cold exposure (at approximately 5 degrees C) improves glucose tolerance despite reducing insulin secretion and increasing energy expenditure. To determine the effects of a small reduction in ambient temperature on energy metabolism, we compared two groups of mice; one exposed to a cool environment (20 degrees C) and the other maintained in a near-thermoneutral environment (25 degrees C) for 10 days. Both glucose-induced insulin secretion and glucose response were significantly impaired in mice exposed to a cool environment. In the cool temperature-exposed mice, skin temperatures were reduced, and plasma norepinephrine levels were increased, suggesting that impairment of insulin secretion was facilitated by induction of sympathetic nervous activity due to skin cooling. In addition, expression of GLUT4 mRNA was increased significantly in inguinal subcutaneous adipose tissue (IWAT) but not in epididymal or brown adipose tissue or skeletal muscle in these mice. Moreover, expression of Dok1, a molecule linked to activation of insulin receptors in adipocyte hypertrophy, and Cd36, a molecule related to NEFA uptake, were also increased at mRNA and/or protein levels only in IWAT of the cool temperature-exposed mice. Fatty acid synthesis was also facilitated, and fat weights were increased only in IWAT from mice kept at 20 degrees C. These results suggest that a small reduction in ambient temperature can affect glucose homeostasis through regulation of insulin secretion and preferentially enhances fat storage in IWAT. These adaptations can be interpreted as preparation for a further reduction in ambient temperature.

Distinct effects of leptin and a melanocortin receptor agonist injected into medial hypothalamic nuclei on glucose uptake in peripheral tissues

OBJECTIVE

The medial hypothalamus mediates leptin-induced glucose uptake in peripheral tissues, and brain melanocortin receptors (MCRs) mediate certain central effects of leptin. However, the contributions of the leptin receptor and MCRs in individual medial hypothalamic nuclei to regulation of peripheral glucose uptake have remained unclear. We examined the effects of an injection of leptin and the MCR agonist MT-II into medial hypothalamic nuclei on glucose uptake in peripheral tissues.

RESEARCH DESIGN AND METHODS

Leptin or MT-II was injected into the ventromedial (VMH), dorsomedial (DMH), arcuate nucleus (ARC), or paraventricular (PVH) hypothalamus or the lateral ventricle (intracerebroventricularly) in freely moving mice. The MCR antagonist SHU9119 was injected intracerebroventricularly. Glucose uptake was measured by the 2-[(3)H]deoxy-d-glucose method.

RESULTS

Leptin injection into the VMH increased glucose uptake in skeletal muscle, brown adipose tissue (BAT), and heart, whereas that into the ARC increased glucose uptake in BAT, and that into the DMH or PVH had no effect. SHU9119 abolished these effects of leptin injected into the VMH. Injection of MT-II either into the VMH or intracerebroventricularly increased glucose uptake in skeletal muscle, BAT, and heart, whereas that into the PVH increased glucose uptake in BAT, and that into the DMH or ARC had no effect.

CONCLUSIONS

The VMH mediates leptin- and MT-II-induced glucose uptake in skeletal muscle, BAT, and heart. These effects of leptin are dependent on MCR activation. The leptin receptor in the ARC and MCR in the PVH regulate glucose uptake in BAT. Medial hypothalamic nuclei thus play distinct roles in leptin- and MT-II-induced glucose uptake in peripheral tissues.

Hypothalamic orexin stimulates feeding-associated glucose utilization in skeletal muscle via sympathetic nervous system

Hypothalamic neurons containing orexin (hypocretin) are activated during motivated behaviors and active waking. We show that injection of orexin-A into the ventromedial hypothalamus (VMH) of mice or rats increased glucose uptake and promoted insulin-induced glucose uptake and glycogen synthesis in skeletal muscle, but not in white adipose tissue, by activating the sympathetic nervous system. These effects of orexin were blunted in mice lacking beta-adrenergic receptors but were restored by forced expression of the beta(2)-adrenergic receptor in both myocytes and nonmyocyte cells of skeletal muscle. Orexin neurons are activated by conditioned sweet tasting and directly excite VMH neurons, thereby increasing muscle glucose metabolism and its insulin sensitivity. Orexin and its receptor in VMH thus play a key role in the regulation of muscle glucose metabolism associated with highly motivated behavior by activating muscle sympathetic nerves and beta(2)-adrenergic signaling.

Role of hypothalamic AMP-kinase in food intake regulation

Adenosine monophosphate-activated protein kinase (AMPK) functions as a cellular fuel gauge that regulates metabolic pathways in nutrient metabolism. Recent studies have strongly implicated that AMPK in the hypothalamus regulates energy metabolism by integrating inputs from multiple hormones, peptides, neurotransmitters, and nutrients. Leptin is an adipocyte hormone that regulates food intake and energy expenditure in peripheral tissues. Leptin inhibits AMPK activity in the arcuate and paraventricular hypothalamus, and its inhibition is necessary for the anorexic effect of leptin. Alteration of hypothalamic AMPK activity is sufficient to change food intake and body weight. Furthermore, fasting/refeeding, glucose, and melanocortin receptor alter AMPK activity in the hypothalamus. Adiponectin has also been shown to increase food intake by activating AMPK in the arcuate hypothalamus. Recent data have shown that acetyl-coenzyme A carboxylase/malonyl-coenzyme A/carnitine palmitoyltransferase-1/fatty acid oxidation and mammalian target of rapamycin signalings are putative downstream pathways for food intake regulation in response to hypothalamic AMPK. Thus, these results suggest that food intake and nutrient metabolism are coordinately regulated by the common signaling pathway of AMPK in the hypothalamus.

Dmbx1 is essential in agouti-related protein action

Dmbx1 is a paired-class homeodomain transcription factor. We show here that mice deficient in Dmbx1 exhibit severe leanness associated with hypophagia and hyperactivity and that isolation of a Dmbx1(-/-) mouse from its cohabitants induces self-starvation, sometimes leading to death, features similar to those of anorexia nervosa in humans. Interestingly, overexpression of agouti in Dmbx1(-/-) mice failed to induce aspects of the A(y)/a phenotype, including hyperphagia, obesity, and diabetes mellitus. In Dmbx1(-/-) mice, administration of agouti-related protein increased cumulative food intake for the initial 6 h but significantly decreased it over 24- and 48-h periods. In addition, Dmbx1 was shown to be expressed at embryonic day 15.5 in the lateral parabrachial nucleus, the rostral nucleus of the tractus solitarius, the dorsal motor nucleus of the vagus, and the reticular nucleus in the brainstem, all of which receive melanocortin signaling, indicating involvement of Dmbx1 in the development of the neural network for the signaling. Thus, Dmbx1 is essential for various actions of agouti-related protein and plays a role in normal regulation of energy homeostasis and behavior.

An increase in murine skeletal muscle peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) mRNA in response to exercise is mediated by beta-adrenergic receptor activation

A single bout of exercise increases expression of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1alpha mRNA, which may promote mitochondrial biogenesis in skeletal muscle. In brown adipose tissue, cold exposure up-regulates PGC-1alpha expression via adrenergic receptor (AR) activation. Because exercise also activates the sympathetic nervous system, we examined whether exercise-induced increase in PGC-1alpha mRNA expression in skeletal muscle was mediated via AR activation. In C57BL/6J mice, injection of the beta2-AR agonist clenbuterol, but not alpha-, beta1-, or beta3-AR agonists, increased PGC-1alpha mRNA expression more than 30-fold in skeletal muscle. The clenbuterol-induced increase in PGC-1alpha mRNA expression in mice was inhibited by pretreatment with the beta-AR antagonist propranolol. In ex vivo experiments, direct exposure of rat epitrochlearis to beta2-AR agonist, but not alpha-, beta1-, and beta3-AR agonist, led to an increase in levels of PGC-1alpha mRNA. Injection of beta2-AR agonist did not increase PGC-1alpha mRNA expression in beta1-, beta2-, and beta3-AR knockout mice (beta-less mice). PGC-1alpha mRNA in gastrocnemius was increased 3.5-fold in response to running on a treadmill for 45 min. The exercise-induced increase in PGC-1alpha mRNA was inhibited by approximately 70% by propranolol or the beta2-AR-specific inhibitor ICI 118,551. The exercise-induced increase in PGC-1alpha mRNA in beta-less mice was also 36% lower than that in wild-type mice. These data indicate that up-regulation of PGC-1alpha expression in skeletal muscle by exercise is mediated, at least in part, by beta-ARs activation. Among ARs, beta2-AR may mediate an increase in PGC-1alpha by exercise.

Adiponectin stimulates AMP-activated protein kinase in the hypothalamus and increases food intake

Adiponectin has been shown to stimulate fatty acid oxidation and enhance insulin sensitivity through the activation of AMP-activated protein kinase (AMPK) in the peripheral tissues. The effects of adiponectin in the central nervous system, however, are still poorly understood. Here, we show that adiponectin enhances AMPK activity in the arcuate hypothalamus (ARH) via its receptor AdipoR1 to stimulate food intake; this stimulation of food intake by adiponectin was attenuated by dominant-negative AMPK expression in the ARH. Moreover, adiponectin also decreased energy expenditure. Adiponectin-deficient mice showed decreased AMPK phosphorylation in the ARH, decreased food intake, and increased energy expenditure, exhibiting resistance to high-fat-diet-induced obesity. Serum and cerebrospinal fluid levels of adiponectin and expression of AdipoR1 in the ARH were increased during fasting and decreased after refeeding. We conclude that adiponectin stimulates food intake and decreases energy expenditure during fasting through its effects in the central nervous system.

Central melanocortin signaling restores skeletal muscle AMP-activated protein kinase phosphorylation in mice fed a high-fat diet

Little is known about the role of the central melanocortin system in the control of fuel metabolism in peripheral tissues. Skeletal muscle AMP-activated protein kinase (AMPK) is activated by leptin and serves as a master regulator of fatty acid beta-oxidation. To elucidate an unidentified role of the central melanocortin system in muscle AMPK regulation, we treated conscious, unrestrained mice intracerebroventricularly with the melanocortin agonist MT-II or the antagonist SHU9119. MT-II augmented phosphorylation of AMPK and its target acetyl-CoA carboxylase (ACC) independent of caloric intake. Conversely, AMPK/ACC phosphorylation by leptin was abrogated by the coadministration of SHU9119 or in KKA(y) mice, which centrally express endogenous melanocortin antagonist. Importantly, high-fat-diet-induced attenuation of AMPK/ACC phosphorylation in leptin-overexpressing transgenic mice was not reversed by central leptin but was markedly restored by MT-II. Our data provide evidence for the critical role of the central melanocortin system in the leptin-skeletal muscle AMPK axis and highlight the system as a therapeutic target in leptin resistance.

Leptin stimulates fatty acid oxidation and peroxisome proliferator-activated receptor alpha gene expression in mouse C2C12 myoblasts by changing the subcellular localization of the alpha2 form of AMP-activated protein kinase

Leptin stimulates fatty acid oxidation in skeletal muscle through the activation of AMP-activated protein kinase (AMPK) and the induction of gene expression, such as that for peroxisome proliferator-activated receptor alpha (PPARalpha). We now show that leptin stimulates fatty acid oxidation and PPARalpha gene expression in the C2C12 muscle cell line through the activation of AMPK containing the alpha2 subunit (alpha2AMPK) and through changes in the subcellular localization of this enzyme. Activated alpha2AMPK containing the beta1 subunit was shown to be retained in the cytoplasm, where it phosphorylated acetyl coenzyme A carboxylase and thereby stimulated fatty acid oxidation. In contrast, alpha2AMPK containing the beta2 subunit transiently increased fatty acid oxidation but underwent rapid translocation to the nucleus, where it induced PPARalpha gene transcription. A nuclear localization signal and Thr(172) phosphorylation of alpha2 were found to be essential for nuclear translocation of alpha2AMPK, whereas the myristoylation of beta1 anchors alpha2AMPK in the cytoplasm. The prevention of alpha2AMPK activation and the change in its subcellular localization inhibited the metabolic effects of leptin. Our data thus suggest that the activation of and changes in the subcellular localization of alpha2AMPK are required for leptin-induced stimulation of fatty acid oxidation and PPARalpha gene expression in muscle cells.

Calcium channel blocker azelnidipine reduces glucose intolerance in diabetic mice via different mechanism than angiotensin receptor blocker olmesartan

The potential combined effect and mechanism of calcium channel blockers (CCB) and angiotensin II type 1 receptor blockers (ARB) to improve insulin resistance were investigated in type 2 diabetic KK-Ay mice, focusing on their antioxidative action. Treatment of KK-Ay mice with a CCB, azelnidipine (3 mg/kg/day), or with an ARB, olmesartan (3 mg/kg/day), for 2 weeks lowered the plasma concentrations of glucose and insulin in the fed state, attenuated the increase in plasma glucose in the oral glucose tolerance test (OGTT), and increased 2-[(3)H]deoxy-d-glucose (2-[(3)H]DG) uptake into skeletal muscle with the increase in translocation of glucose transporter 4 (GLUT4) to the plasma membrane. Both blockers also decreased the in situ superoxide production in skeletal muscle. The decrease in plasma concentrations of glucose and insulin in the fed state and superoxide production in skeletal muscle, as well as GLUT4 translocation to the plasma membrane, after azelnidipine administration was not significantly affected by coadministration of an antioxidant, 2,2,6,6-tetramethyl-1-piperidinyloxy (tempol). However, those changes caused by olmesartan were further improved by tempol. Moreover, olmesartan enhanced the insulin-induced tyrosine phosphorylation of insulin receptor substrate-1 induced in skeletal muscle, whereas azelnidipine did not change it. Coadministration of azelnidipine and olmesartan further decreased the plasma concentrations of glucose and insulin, improved OGTT, and increased 2-[(3)H]DG uptake in skeletal muscle. These results suggest that azelnidipine improved glucose intolerance mainly through inhibition of oxidative stress and enhanced the inhibitory effects of olmesartan on glucose intolerance, as well as the clinical possibility that the combination of CCB and ARB could be more effective than monotherapy in the treatment of insulin resistance.

Deletion of Angiotensin II Type 2 Receptor Exaggerated Atherosclerosis in Apolipoprotein E–Null Mice

Background— The role of angiotensin II (Ang II) type 2 (AT 2 ) receptor in atherosclerosis was explored with the use of AT 2 receptor/apolipoprotein E (ApoE)–double-knockout (AT 2 /ApoE-DKO) mice, with a focus on oxidative stress.

Methods and Results— After treatment with a high-cholesterol diet (1.25% cholesterol) for 10 weeks, ApoE-knockout (KO) mice developed atherosclerotic lesions in the aorta. In AT 2 /ApoE-DKO mice receiving a high-cholesterol diet, the atherosclerotic changes were further exaggerated, without significant changes in plasma cholesterol level and blood pressure. In the atherosclerotic lesion, an increase in superoxide production, NADPH oxidase activity, and expression of p47 phox was observed. These changes were also greater in AT 2 /ApoE-DKO mice. An Ang II type 1 (AT 1 ) receptor blocker, valsartan, inhibited atherosclerotic lesion formation, superoxide production, NADPH oxidase activity, and p47 phox expression; these inhibitory effects were significantly weaker in AT 2 /ApoE-KO mice. We further examined the signaling mechanism of the AT 2 receptor–mediated antioxidative effect in cultured fetal vascular smooth muscle cells. NADPH oxidase activity and phosphorylation and translocation of p47 phox induced by Ang II were inhibited by valsartan but enhanced by an AT 2 receptor blocker, PD123319.

Conclusions— These results suggest that AT 2 receptor stimulation attenuates atherosclerosis through inhibition of oxidative stress and that the antiatherosclerotic effect of valsartan could be at least partly due to AT 2 receptor stimulation by unbound Ang II.

Possible Inhibition of Focal Cerebral Ischemia by Angiotensin II Type 2 Receptor Stimulation

Background— The role of angiotensin II receptor subtypes was investigated in focal brain ischemia induced by middle cerebral artery (MCA) occlusion.

Methods and Results— In Agtr2 + (wild-type) mice, MCA occlusion induced focal ischemia of ≈20% to 30% of the total area in coronal section of the brain. The ischemic area was significantly larger in angiotensin II type 2 receptor–deficient ( Agtr2 − ) mice than in Agtr2 + mice. The neurological deficit after MCA occlusion was also greater in Agtr2 − mice than in Agtr2 + mice. The decrease in surface cerebral blood flow after MCA occlusion was significantly exaggerated in the peripheral region of the MCA territory in Agtr2 − mice. Superoxide production and NADPH oxidase activity were enhanced in the ischemic area of the brain in Agtr2 − mice. An AT 1 receptor blocker, valsartan, at a nonhypotensive dose significantly inhibited the ischemic area, neurological deficit, and reduction of cerebral blood flow as well as superoxide production and NADPH oxidase activity in Agtr2 + mice. These inhibitory actions of valsartan were weaker in Agtr2 − mice.

Conclusions— These results suggest that AT 2 receptor stimulation has a protective effect on ischemic brain lesions, at least partly through the modulation of cerebral blood flow and superoxide production.

Roles of angiotensin type 1 and 2 receptors in pregnancy-associated blood pressure change

BACKGROUND

Activation of the renin-angiotensin system with increased levels of renin and angiotensin (Ang) II in pregnancy has been reported, but the vascular responsiveness to Ang II seems to be decreased, thereby keeping maternal blood pressure (BP) constant. We postulated that the balance of angiotensin type 1 (AT1) and angiotensin type 2 (AT2) receptor expression, which would exert antagonistic actions on vasoconstriction and cell growth, might control BP in pregnancy.

METHODS

Using wild type (C57BL/6J), AT1a receptor null and AT2 receptor null mice, we examined the changes in BP, expression and localization of AT1 and AT2 receptors in placenta, umbilical cord, and uterus by immunohistochemical staining and urinary albumin measurement during pregnancy.

RESULTS

Wild type mice did not show any significant change in BP throughout pregnancy. The BP in AT1a receptor null mice declined significantly in the second trimester of pregnancy, whereas BP in AT2 receptor null mice increased significantly in the third trimester. We did not observe any significant differences in albuminuria, litter size, or body weight of neonates among the three groups. Vascular smooth muscle cells in blood vessels of the umbilical cord and placenta specifically expressed AT2 receptors, which are minimally expressed in adult vessels. In contrast, AT1 receptors were dominantly expressed in the cytotrophoblast and chorionic plate as well as blood vessels in placenta and umbilical cord.

CONCLUSIONS

Our results suggested that disturbance of the balance of the AT1 and AT2 receptors could trigger pregnancy induced hypertension.

Angiotensin II type-1 receptor blocker valsartan enhances insulin sensitivity in skeletal muscles of diabetic mice

Angiotensin II has been shown to contribute to the pathogenesis of insulin resistance; however, the mechanism is not well understood. The present study was undertaken to investigate the potential effect of an angiotensin II type-1 (AT1) receptor blocker, valsartan, to improve insulin resistance and to explore the signaling basis of cross-talk of the AT1 receptor- and insulin-mediated signaling in type 2 diabetic KK-Ay mice. Treatment of KK-Ay mice with valsartan at a dose of 1 mg/kg per day, which did not influence systolic blood pressure, significantly increased insulin-mediated 2-[3H]deoxy-d-glucose (2-[3H]DG) uptake into skeletal muscle and attenuated the increase in plasma glucose concentration after a glucose load and plasma concentrations of glucose and insulin. In contrast, insulin-mediated 2-[3H]DG uptake into skeletal muscle was not influenced in AT2 receptor null mice, and an AT2 receptor blocker, PD123319, did not affect 2-[3H]DG uptake and superoxide production in skeletal muscle of KK-Ay mice. Moreover, we observed that valsartan treatment exaggerated the insulin-induced phosphorylation of IRS-1, the association of IRS-1 with the p85 regulatory subunit of phosphoinositide 3 kinase (PI 3-K), PI 3-K activity, and translocation of GLUT4 to the plasma membrane. It also reduced tumor necrosis factor-alpha (TNF-alpha) expression and superoxide production in skeletal muscle of KK-Ay mice. Specific AT1 receptor blockade increases insulin sensitivity and glucose uptake in skeletal muscle of KK-Ay mice via stimulating the insulin signaling cascade and consequent enhancement of GLUT4 translocation to the plasma membrane.

Regulation of Inhibitory Protein-κB and Monocyte Chemoattractant Protein-1 by Angiotensin II Type 2 Receptor-Activated Src Homology Protein Tyrosine Phosphatase-1 in Fetal Vascular Smooth Muscle Cells

In the present study we examined the effects of angiotensin II (Ang II) type 2 (AT(2)) receptor stimulation on AT(1) receptor-mediated monocyte chemoattractant protein-1 (MCP-1) expression and the possible mechanisms of AT(2) receptor-mediated signaling in cultured rat fetal vascular smooth muscle cells, which express both AT(1) and AT(2) receptors. Ang II stimulation induced MCP-1 mRNA expression as well as an increase in nuclear factor-kappaB (NF-kappaB) binding to the corresponding cis DNA element of the MCP-1 promoter region and a decrease in the cytosolic inhibitory protein-kappaB (IkappaB) protein level via AT(1) receptor stimulation, whereas stimulation of the AT(2) receptor decreased Ang II-induced MCP-1 expression, NF-kappaB DNA binding, and IkappaB degradation, suggesting that activation of the AT(2) receptor attenuated AT(1) receptor-mediated MCP-1 expression via a decrease in NF-kappaB DNA binding and an increase in IkappaB stability. Moreover, we demonstrated that AT(2) receptor stimulation attenuated TNFalpha-mediated NF-kappaB activation and MCP-1 expression. A tyrosine phosphatase inhibitor, orthovanadate, attenuated the AT(2) receptor-mediated increase in IkappaB protein. Moreover, we observed that two IkappaB subunits (IkappaBalpha and IkappaBbeta) were tyrosine-phosphorylated after Ang II stimulation. Transfection of a dominant-negative Src homology protein tyrosine phosphatase-1 mutant into vascular smooth muscle cells inhibited the AT(2) receptor-mediated increase in IkappaB, leading to a significant increase in AT(1) receptor-induced NF-kappaB activation and MCP-1 expression. Taken together, our results demonstrated that AT(2) receptor stimulation attenuated MCP-1 expression via IkappaB stabilization, and Src homology protein tyrosine phosphatase-1 might play a critical role in the transcriptional regulation of MCP-1 expression through the control of IkappaB protein stability.

Nicotine Enhances Angiotensin II-Induced Mitogenic Response in Vascular Smooth Muscle Cells and Fibroblasts

Objective— The pathogenetic mechanism of tobacco-related cardiovascular diseases is still not well defined. We examined the potential possibility of an interaction between nicotine, a major component of cigarette smoke, and angiotensin II (Ang II), which plays an important role in the pathogenesis of cardiovascular diseases characterized by Ang II type 1 (AT 1 ) receptor-mediated abnormal growth of vascular smooth muscle cells (VSMC) and fibroblasts.

Methods and Results— Nicotine or Ang II-stimulated [ 3 H]thymidine incorporation and c-fos expression in adult rat aortic VSMC and adventitial fibroblast. The nicotine-induced DNA synthesis was not affected by valsartan, an AT 1 receptor-specific blocker, or PD123319, an Ang II type 2 (AT 2 ) receptor-specific antagonist. Nicotine or Ang II stimulation rapidly increased extracellular signal-regulated kinase (ERK) activation, tyrosine- and serine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3, and p38 mitogen-activated protein kinase (p38 MAPK), in both cell types. Interestingly, co-administration of nicotine and Ang II at lower doses, which did not affect cell growth, induced DNA synthesis and c-fos expression accompanied by enhancement of ERK, STAT, and p38MAPK activity. PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor, or SB23058, a p38MAPK inhibitor, significantly attenuated the vasotrophic effect of nicotine and Ang II.

Conclusions— These results suggest that nicotine exerts a growth-promoting effect on vascular cells and enhances the Ang II-induced vasotrophic effect, which is at least partly mediated by the activation of ERK, STAT, and p38MAPK.

Regulation of collagen synthesis in mouse skin fibroblasts by distinct angiotensin II receptor subtypes

We examined the possibility of whether angiotensin (Ang) II type 1 (AT1) and type 2 (AT2) receptor stimulation differentially regulates collagen production in mouse skin fibroblasts. Both AT1 and AT2 receptors were expressed in neonatal skin fibroblasts prepared from wild-type mice to a similar degree, and the AT1a receptor was exclusively expressed as opposed to the AT1b receptor. In wild-type fibroblasts, Ang II increased collagen synthesis accompanied by an increase in expression of tissue inhibitor of metalloproteinase (TIMP)-1, and these increases were inhibited by valsartan, an AT1 receptor blocker, but augmented by PD123319, an AT2 receptor antagonist. Ang II decreased basal and IGF-I-induced collagen production and inhibited TIMP-1 expression in neonatal skin fibroblasts prepared from AT1a knockout (KO) mice. These Ang II-mediated inhibitory effects on collagen production and TIMP-1 expression observed in AT1a KO fibroblasts were attenuated by the addition of PD123319 or a tyrosine phosphatase inhibitor, sodium orthovanadate, but not affected by a serine/threonine phosphatase inhibitor, okadaic acid. Moreover, we demonstrated that transfection of a catalytically inactive, dominant negative SHP-1 (Src homology 2-containing protein-tyrosine phosphatase-1) mutant inhibited the Ang II-mediated inhibitory effect on both collagen synthesis and TIMP-1 expression in AT1a KO fibroblasts. These results suggest that AT1a receptor stimulation increases collagen production in skin fibroblasts at least in part due to the inhibition of collagen degradation via the increase in TIMP-1 expression, whereas AT2 receptor stimulation exerts inhibitory effects on TIMP-1 expression, which is mediated at least partially by the activation of SHP-1, thereby possibly inhibiting collagen production.

Important role of nitric oxide in the effect of angiotensin-converting enzyme inhibitor imidapril on vascular injury

To examine the possible role of the bradykinin-NO system in the action of ACE inhibitors, we studied the effects of imidapril, an ACE inhibitor, on inflammatory vascular injury by using AT1a-receptor-deficient (AT1aKO) mice. A polyethylene cuff was placed around the femoral artery of AT1aKO mice and wild-type (WT; C57BL/6J) mice. Neointimal area in cross sections of the artery was measured 14 days after cuff placement. A low dose of imidapril (1 mg/kg per day), which did not affect blood pressure, was administered by gavage. Expression of monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha was detected by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR) 7 days after the operation. Neointimal formation, vascular smooth muscle cell proliferation, and expression of MCP-1 and TNF-alpha were attenuated in the injured artery in AT1aKO mice compared with those in WT mice. Imidapril inhibited neointimal formation, DNA synthesis of vascular smooth muscle cells, and expression of MCP-1 and TNF-alpha in AT1aKO mice as well as in WT mice. In addition, imidapril increased tissue cGMP content after cuff placement. These inhibitory effects of imidapril were significantly reduced or abolished by a bradykinin receptor antagonist, Hoechst 140, or an NO synthase inhibitor, L-NAME, both in WT and AT1aKO mice. Treatment with imidapril did not change AT2 receptor and ACE expression detected by RT-PCR in the injured artery. These results indicate that not only blockade of angiotensin II production but also activation of the bradykinin-NO system plays an important role in the beneficial effects of imidapril on vascular remodeling.