Brain and muscle Arnt-like protein-1 (BMAL1; also known as MOP3 or Arnt3) is a transcription factor known to regulate circadian rhythm. Here, we established its involvement in the control of adipogenesis and lipid metabolism activity in mature adipocytes. During adipose differentiation in 3T3-L1 cells, the level of BMAL1 mRNA began to increase 4 days after induction and was highly expressed in differentiated cells. In white adipose tissues isolated from C57BL͞6J mice, BMAL1 was predominantly expressed in a fraction containing adipocytes, as compared with the stromalvascular fraction. BMAL1 knockout mice embryonic fibroblast cells failed to be differentiated into adipocytes. Importantly, adding BMAL1 back by adenovirus gene transfer restored the ability of BMAL1 knockout mice embryonic fibroblast cells to differentiate. Knock-down of BMAL1 expression in 3T3-L1 cells by an RNA interference technique allowed the cells to accumulate only minimum amounts of lipid droplets in the cells. Adenovirus-mediated expression of BMAL1 in 3T3-L1 adipocytes resulted in induction of several factors involved in lipogenesis. The promoter activity of these genes was stimulated in a BMAL1-dependent manner. Interestingly, expression of these factors showed clear circadian rhythm in mice adipose tissue. Furthermore, overexpression of BMAL1 in adipocytes increased lipid synthesis activity. These results indicate that BMAL1, a master regulator of circadian rhythm, also plays important roles in the regulation of adipose differentiation and lipogenesis in mature adipocytes.circadian rhythm A dipocytes play essential metabolic roles not only serving as massive energy reserves but also secreting hormones and cytokines that regulate metabolic activities (1, 2). The link between metabolic activity in adipocytes and circadian rhythm has long been studied; e.g., glucose and lipid homeostasis are well known to exhibit circadian variation (3-6). More recently, circadian expression of adiponectin receptors in adipocytes was reported (7). Therefore, molecular clock may play important roles in the regulation of metabolic activity in adipocytes. In a previous study, we reported that white adipose tissue contains functional molecular clock and that expression of several adipocytokines, including leptin, and plasminogen activator inhibitor-1 display circadian rhythm (8). The diurnal rhythm in the level of these molecules suggests that the molecular clock is at least partly associated with the onset of metabolic syndrome.The molecular clock is composed of transcriptional feedback loops in organisms ranging from cyanobacteria to humans. Brain and muscle Arnt-like protein-1 [BMAL1; also referred to as MOP3 (9) or Arnt3 (10)] is a transcription factor playing central roles in the regulation of circadian rhythms (11). BMAL1 forms heterodimers with another basic helix-loop-helix͞PAS protein, CLOCK, which drives transcription from E-box elements found in the promoter of circadian responsive genes, including period (Per)1 and cryptochrome (Cry). After translati...

SUMMARY Thiazolidinediones (TZDs) are PPARγ activators that exhibit vasculoprotective properties. To determine the vascular function of PPARγ, we analyzed Tie2Cre/flox and SM22Cre/flox mice. Unexpectedly, both knockout strains exhibited a significant reduction of circadian variations in blood pressure and heart rate in parallel with diminished variations in urinary norepinephrine/epinephrine excretion and impaired rhythmicity of the canonical clock genes including Bmal1. PPARγ expression in the aorta exhibited a robust rhythmicity with a more than 20-fold change during the light/dark cycle. Rosiglitazone treatment induced aortic expression of Bmal1 mRNA, and ChIP and promoter assays revealed that Bmal1 is a direct PPARγ target gene. These studies have uncovered a role for vascular PPARγ as a peripheral factor participating in regulation of cardiovascular rhythms.

Cardiac mammalian target of rapamycin (mTOR) is necessary and sufficient to prevent cardiac dysfunction in pathological hypertrophy. However, the role of cardiac mTOR in heart failure after ischemic injury remains undefined. To address this question, we used transgenic (Tg) mice with cardiac-specific overexpression of mTOR (mTOR-Tg mice) to study ischemia-reperfusion (I/R) injury in two animal models: 1) in vivo I/R injury with transient coronary artery ligation and 2) ex vivo I/R injury in Langendorff-perfused hearts with transient global ischemia. At 28 days after I/R, mortality was lower in mTOR-Tg mice than littermate control mice [wild-type (WT) mice]. Echocardiography and MRI demonstrated that global cardiac function in mTOR-Tg mice was preserved, whereas WT mice exhibited significant cardiac dysfunction. Masson's trichrome staining showed that 28 days after I/R, the area of interstitial fibrosis was smaller in mTOR-Tg mice compared with WT mice, suggesting that adverse left ventricular remodeling is inhibited in mTOR-Tg mice. In the ex vivo I/R model, mTOR-Tg hearts demonstrated improved functional recovery compared with WT hearts. Perfusion with Evans blue after ex vivo I/R yielded less staining in mTOR-Tg hearts than WT hearts, indicating that mTOR overexpression inhibited necrosis during I/R injury. Expression of proinflammatory cytokines, including IL-6 and TNF-α, in mTOR-Tg hearts was lower than in WT hearts. Consistent with this, IL-6 in the effluent post-I/R injury was lower in mTOR-Tg hearts than in WT hearts. These findings suggest that cardiac mTOR overexpression in the heart is sufficient to provide substantial cardioprotection against I/R injury and suppress the inflammatory response.

Heart failure, a major symptom in the progression of cardiac hypertrophy, is a critical risk factor for cardiac death. A large body of research has investigated cardioprotective mechanisms that prevent or minimize hypertrophy, identifying a variety of specific peptide hormones, growth factors, and cytokines with cardioprotective properties. Recent investigation of the downstream effector pathways for these growth factors has identified molecules involved in the progression of cardiac hypertrophy and heart failure, including phosphoinositide 3-kinase (PI3K), Akt and mammalian target of rapamycin (mTOR). Using genetically modified transgenic or knockout mice and adenoviral targeting to manipulate expression or function in experimental models of heart failure, several investigators have demonstrated that the PI3K-Akt pathway regulates cardiomyocyte size, survival, angiogenesis, and inflammation in both physiological and pathological cardiac hypertrophy. In this review, we discuss the reciprocal regulation of PI3K, Akt and mTOR in cardiomyocytes and their association with cardiac disease.

Arginine-vasopressin (AVP) is known to be involved in maintaining glucose homeostasis, and AVP-resistance is observed in poorly controlled non-insulin-dependent diabetes mellitus subjects, resulting in a lowered plasma volume. Recently we reported that V1a vasopressin receptor-deficient (V1aR ؊/؊ ) mice exhibited a decreased circulating blood volume and hypermetabolism of fat accompanied with impaired insulin-signaling. Here we further investigated the roles of the AVP/V1a receptor in regulating glucose homeostasis and plasma volume using V1aR؊/؊ mice. The plasma glucose levels at the baseline or during a glucose tolerance test were higher in V1aR ؊/؊ than wild-type (WT) mice. Moreover, a hyperinsulinemic-euglycemic clamp revealed that the glucose infusion rate was significantly lower in V1aR ؊/؊ mice than in WT mice and that hepatic glucose production was higher in V1aR ؊/؊ mice than WT mice. In contrast to the increased hepatic glucose production, the liver glycogen content was decreased in the mutant mice. These results indicated that the mutant mice had impaired glucose tolerance. Furthermore, feeding V1aR ؊/؊ mice a high-fat diet accompanied by increased calorie intake resulted in significantly overt obesity in comparison with WT mice. In addition, we found that the circulating plasma volume and aldosterone level were decreased in V1aR ؊/؊ mice, although the plasma AVP level was increased. These results suggested that the effect of AVP on water recruitment was disturbed in V1aR ؊/؊ mice. Thus, we demonstrated that one of the AVP-resistance conditions resulting from deficiency of the V1a receptor leads to decreased plasma volume as well as impaired glucose homeostasis, which can progress to obesity under conditions of increased calorie intake. (Endocrinology 148: 2075-2084, 2007)A RGININE-VASOPRESSIN (AVP) is a neuropeptide hormone that is involved in diverse functions, including the regulation of osmotic homeostasis, vasoconstriction, and ACTH release. These physiological effects are mediated by three types of AVP receptors, designated as V1a, V1b, and V2 (1-3). The V1a receptor is widely expressed, whereas the V1b and V2 receptors are predominantly expressed in the anterior pituitary and the kidney, respectively (1-4). The functional role of the V1a receptor is considered to mediate vascular contraction (5), cellular proliferation (6), platelet aggregation (7), and glycogenolysis (1, 8). The V1b receptor stimulates ACTH and insulin release (9, 10). Both V1a and V1b receptors bind to the Gq protein and act through phosphatidylinositol hydrolysis to mobilize intercellular Ca 2ϩ (11,12). The V2 receptor is coupled with the Gs protein and stimulates adenylate cyclase to increase cellular cAMP, which results in the induction of an antidiuretic effect in the kidney (13).There have been several reports indicating the involvement of AVP in regulating the plasma glucose homeostasis. The plasma AVP level was increased in patients with insulindependent diabetes mellitus (IDDM) or non-IDDM (NIDDM) (14, 15), and treati...