Rie Yamamoto

Pericardial fat accumulation in men as a risk factor for coronary artery disease

An increment of abdominal visceral fat accumulation has been reported to be a coronary risk factor. We determined the predictive power of pericardial fat (Pfat) accumulation as intra-thoracic visceral fat, in the diagnosis of coronary artery disease (CAD). Among 251 (181 non-obese [body mass index<25], 70 obese [body mass index> or =25]) Japanese male patients who underwent computed tomography (CT), 128 (90 non-obese, 38 obese) patients were suffering from CAD. Pfat volume was determined by the sum of cross-sectional images 1cm thick from the atrial appendage to the apex over the diaphragm. Abdominal visceral fat (Vfat) and subcutaneous fat (Sfat) areas were measured by a single scan at the L4-L5 region. Pfat was most associated with Vfat in body fat distribution. In non-obese patients, Pfat was most associated with CAD among the various risk factors including body fat distribution. Moreover, Pfat was the strongest independent variable for the severity of CAD, determined by coronary angiogram. This result showed that pericardial fat accumulation was a stronger coronary risk factor than the other body fat distributions in non-obese men.

Cardiac mast cells cause atrial fibrillation through PDGF-A–mediated fibrosis in pressure-overloaded mouse hearts

Atrial fibrillation (AF) is a common arrhythmia that increases the risk of stroke and heart failure. Here, we have shown that mast cells, key mediators of allergic and immune responses, are critically involved in AF pathogenesis in stressed mouse hearts. Pressure overload induced mast cell infiltration and fibrosis in the atrium and enhanced AF susceptibility following atrial burst stimulation. Both atrial fibrosis and AF inducibility were attenuated by stabilization of mast cells with cromolyn and by BM reconstitution from mast cell-deficient WBB6F1-KitW/W-v mice. When cocultured with cardiac myocytes or fibroblasts, BM-derived mouse mast cells increased platelet-derived growth factor A (PDGF-A) synthesis and promoted cell proliferation and collagen expression in cardiac fibroblasts. These changes were abolished by treatment with a neutralizing antibody specific for PDGF alpha-receptor (PDGFR-alpha). Consistent with these data, upregulation of atrial Pdgfa expression in pressure-overloaded hearts was suppressed by BM reconstitution from WBB6F1-KitW/W-v mice. Furthermore, injection of the neutralizing PDGFR-alpha-specific antibody attenuated atrial fibrosis and AF inducibility in pressure-overloaded hearts, whereas administration of homodimer of PDGF-A (PDGF-AA) promoted atrial fibrosis and enhanced AF susceptibility in normal hearts. Our results suggest a crucial role for mast cells in AF and highlight a potential application of controlling the mast cell/PDGF-A axis to achieve upstream prevention of AF in stressed hearts.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors prevent the development of cardiac hypertrophy and heart failure in rats

OBJECTIVES The aim of the present study was to determine whether 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have preventive effects on the development of cardiac hypertrophy and heart failure. BACKGROUND Statins have been reported to have various pleiotropic effects, such as inhibition of inflammation and cell proliferation. METHODS Dahl rats were divided into three groups: LS, the rats fed the low-salt diet (0.3% NaCl); HS, the rats fed the high-salt diet (8% NaCl) from the age of 6 weeks; and CERI, the rats fed the high-salt diet with cerivastatin 1 mg/kg/d by gavage from the age of 6 weeks. RESULTS In HS rats, cardiac function was markedly impaired and all rats showed the signs of heart failure within 17 weeks of age. In CERI rats, cardiac function was better than that of HS and no rats were dead up to 17 weeks of age. The development of cardiac hypertrophy and fibrosis was attenuated, and the number of apoptotic cells and expression of proinflammatory cytokine interleukin (IL)-1beta gene were less as compared with HS rats. Pretreatment of cerivastatin suppressed the adriamycin-induced apoptosis of cultured cardiomyocytes of neonatal rats. CONCLUSIONS These results suggest that statins have a protective effect on cardiac myocytes and may be useful to prevent the development of hypertensive heart failure.

PDK1 coordinates survival pathways and β-adrenergic response in the heart

The 3-phosphoinositide-dependent kinase-1 (PDK1) plays an important role in the regulation of cellular responses in multiple organs by mediating the phosphoinositide 3-kinase (PI3-K) signaling pathway through activating AGC kinases. Here we defined the role of PDK1 in controlling cardiac homeostasis. Cardiac expression of PDK1 was significantly decreased in murine models of heart failure. Tamoxifen-inducible and heart-specific disruption of Pdk1 in adult mice caused severe and lethal heart failure, which was associated with apoptotic death of cardiomyocytes and β1-adrenergic receptor (AR) down-regulation. Overexpression of Bcl-2 protein prevented cardiomyocyte apoptosis and improved cardiac function. In addition, PDK1-deficient hearts showed enhanced activity of PI3-Kγ, leading to robust β1-AR internalization by forming complex with β-AR kinase 1 (βARK1). Interference of βARK1/PI3-Kγ complex formation by transgenic overexpression of phosphoinositide kinase domain normalized β1-AR trafficking and improved cardiac function. Taken together, these results suggest that PDK1 plays a critical role in cardiac homeostasis in vivo by serving as a dual effector for cell survival and β-adrenergic response.

Agonist-Independent Constitutive Activity of Angiotensin II Receptor Promotes Cardiac Remodeling in Mice

The angiotensin II (Ang II) type 1 (AT1) receptor mainly mediates the physiological and pathological actions of Ang II, but recent studies have suggested that AT1 receptor inherently shows spontaneous constitutive activity even in the absence of Ang II in culture cells. To elucidate the role of Ang II–independent AT1 receptor activation in the pathogenesis of cardiac remodeling, we generated transgenic mice overexpressing AT1 receptor under the control of &agr;-myosin heavy chain promoter in angiotensinogen-knockout background (AT1Tg-AgtKO mice). In AT1Tg-AgtKO hearts, redistributions of the G&agr;q11 subunit into cytosol and phosphorylation of extracellular signal-regulated kinases were significantly increased, compared with angiotensinogen-knockout mice hearts, suggesting that the AT1 receptor is constitutively activated independent of Ang II. As a consequence, AT1Tg-AgtKO mice showed spontaneous systolic dysfunction and chamber dilatation, accompanied by severe interstitial fibrosis. Progression of cardiac remodeling in AT1Tg-AgtKO mice was prevented by treatment with candesartan, an inverse agonist for the AT1 receptor, but not by its derivative candesartan-7H, deficient of inverse agonism attributed to a lack of the carboxyl group at the benzimidazole ring. Our results demonstrate that constitutive activity of the AT1 receptor under basal conditions contributes to the cardiac remodeling even in the absence of Ang II, when the AT1 receptor is upregulated in the heart.

Angiotensin II Type 1 Receptor Signaling Regulates Feeding Behavior through Anorexigenic Corticotropin-releasing Hormone in Hypothalamus

The activation of renin-angiotensin system contributes to the development of metabolic syndrome and diabetes as well as hypertension. However, it remains undetermined how renin-angiotensin system is implicated in feeding behavior. Here, we show that angiotensin II type 1 (AT1) receptor signaling regulates the hypothalamic neurocircuit that is involved in the control of food intake. Compared with wild-type Agtr1a+/+ mice, AT1 receptor knock-out (Agtr1a−/−) mice were hyperphagic and obese with increased adiposity on an ad libitum diet, whereas Agtr1a−/− mice were lean with decreased adiposity on a pair-fed diet. In the hypothalamus, mRNA levels of anorexigenic neuropeptide corticotropin-releasing hormone (Crh) were lower in Agtr1a−/− mice than in Agtr1a+/+ mice both on an ad libitum and pair-fed diet. Furthermore, intracerebroventricular administration of CRH suppressed food intake both in Agtr1a+/+ and Agtr1a−/− mice. In addition, the Crh gene promoter was significantly transactivated via the cAMP-responsive element by angiotensin II stimulation. These results thus demonstrate that central AT1 receptor signaling plays a homeostatic role in the regulation of food intake by maintaining gene expression of Crh in hypothalamus and suggest a therapeutic potential of central AT1 receptor blockade in feeding disorders.

Multivalent ligand-receptor interactions elicit inverse agonist activity of AT(1) receptor blockers against stretch-induced AT(1) receptor activation.

Type 1 angiotensin II (AT1) receptor has a critical role in the development of load-induced cardiac hypertrophy. Recently, we showed that mechanical stretching of cells activates the AT1 receptor without the involvement of angiotensin II (AngII) and that this AngII-independent activation is inhibited by the inverse agonistic activity of the AT1 receptor blocker (ARB), candesartan. Although the inverse agonist activity of ARBs has been studied in terms of their action on constitutively active AT1 receptors, the structure–function relationship of the inverse agonism they exert against stretch-induced AT1 receptor activation has not been fully elucidated. Assays evaluating c-fos gene expression and phosphorylated extracellular signal-regulated protein kinases (ERKs) have shown that olmesartan has strong inverse agonist activities against the constitutively active AT1 receptor and the stretch-induced activation of AT1 receptor, respectively. Ternary drug–receptor interactions, which occur between the hydroxyl group of olmesartan and Tyr113 and between the carboxyl group of olmesartan and Lys199 and His256, were essential for the potent inverse agonist action olmesartan exerts against stretch-induced ERK activation and the constitutive activity of the AT1-N111G mutant receptor. Furthermore, the inverse agonist activity olmesartan exerts against stretch-induced ERK activation requires an additional drug–receptor interaction involving the tetrazole group of olmesartan and Gln257 of the AT1 receptor. These results suggest that multivalent interactions between an inverse agonist and the AT1 receptor are required to stabilize the receptor in an inactive conformation in response to the distinct processes that lead to an AngII-independent activation of the AT1 receptor.

Angiotensin II receptor blockade promotes repair of skeletal muscle through down-regulation of aging-promoting C1q expression.

Disruption of angiotensin II type 1 (AT1) receptor prolonged life span in mice. Since aging-related decline in skeletal muscle function was retarded in Atgr1a−/− mice, we examined the role of AT1 receptor in muscle regeneration after injury. Administration of AT1 receptor blocker irbesartan increased the size of regenerating myofibers, decreased fibrosis, and enhanced functional muscle recovery after cryoinjury. We recently reported that complement C1q, secreted by macrophages, activated Wnt/β-catenin signaling and promoted aging-related decline in regenerative capacity of skeletal muscle. Notably, irbesartan induced M2 polarization of macrophages, but reduced C1q expression in cryoinjured muscles and in cultured macrophage cells. Irbesartan inhibited up-regulation of Axin2, a downstream gene of Wnt/β-catenin pathway, in cryoinjured muscles. In addition, topical administration of C1q reversed beneficial effects of irbesartan on skeletal muscle regeneration after injury. These results suggest that AT1 receptor blockade improves muscle repair and regeneration through down-regulation of the aging-promoting C1q-Wnt/β-catenin signaling pathway.

Single amino acid substitution in the V3 domain of CD4 is responsible for OKT4 epitope deficiency

The CD4 molecule is a non-polymorphic T-cell differentiation antigen expressed on the cell surface of thymocytes and on the subpopulation of mature T cells whose antigen recognition is restricted by the class II major histocompatibility complex (MHC). CD4 is thought to play a role in antigen recognition by binding to the class II MHC and by transducing signals via the src-related tyrosine kinase, p56 lck (Rudd et al. 1989). Molecular cloning of the CD4 gene revealed that it encodes a 433 amino acid protein with four immunoglobulin V-region-like domains (Maddon et al. 1985). Of major importance for understanding the pathogenesis of acquired immune deficiency syndrome (AIDS), CD4 is also the receptor for human immuno-deficiency virus (HIV; Dalgleish et al. 1986; Klatzmann et al. 1986). Bach and co-workers (1981) described patients in which the OKT4 reactive epitope of the CD4 molecule was absent while other characteristic epitopes were present. Now known as OKT4 epitope deficiency (OED), this condition may reflect polymorphism within the CD4 molecule. Subsequent studies revealed an autosomal codominant mode of inheritance (Stohl and Kunkel 1984). The incidence of OED is relatively high in African Americans (8.3 % ; Fuller et al. 1984; Casey et al. 1986), and low in Japanese (0.43 %; Aozasa et al. 1985), and it is rare in Caucasians. Here we report a case of familial OED in a Japanese family in which phenotypes of the father and son show complete absence of the OKT4 epitope while those of the mother and daughter show the epitope at reduced levels that are half the normal value. Figure la shows results of the fluorescence-activated cell sorter (FACS) two-color analysis of peripheral blood mononuclear cells obtained from a normal and a case of