Ken-ichi Aihara

Suppressive function of androgen receptor in bone resorption.

As locally converted estrogen from testicular testosterone contributes to apparent androgen activity, the physiological significance of androgen receptor (AR) function in the beneficial effects of androgens on skeletal tissues has remained unclear. We show here that inactivation of AR in mice using a Cre-loxP system-mediated gene-targeting technique caused bone loss in males but not in females. Histomorphometric analyses of 8-week-old male AR knockout (ARKO) mice showed high bone turnover with increased bone resorption that resulted in reduced trabecular and cortical bone mass without affecting bone shape. Bone loss in orchidectomized male ARKO mice was only partially prevented by treatment with aromatizable testosterone. Analysis of primary osteoblasts and osteoclasts from ARKO mice revealed that AR function was required for the suppressive effects of androgens on osteoclastogenesis supporting activity of osteoblasts but not on osteoclasts. Furthermore, expression of the receptor activator of NF-κB ligand (RANKL) gene, which encodes a major osteoclastogenesis inducer, was found to be up-regulated in osteoblasts from AR-deficient mice. Our results indicate that AR function is indispensable for male-type bone formation and remodeling.

Disruption of Nuclear Vitamin D Receptor Gene Causes Enhanced Thrombogenicity in Mice

Vitamin D metabolites influence the expression of various genes involved in calcium homeostasis, cell differentiation, and regulation of the immune system. Expression of these genes is mediated by the activation of the nuclear vitamin D receptor (VDR). Previous studies have shown that a hormonally active form of vitamin D, 1α,25-dihydroxyvitamin D3, exerts anticoagulant effects in cultured monocytic cells. To clarify whether activation of VDR plays any antithrombotic actions in vivo, hemostatic/thrombogenic systems were examined in normocalcemic VDR knock-out (KO) mice on a high calcium diet and compared with wild type and hypocalcemic VDRKO mice that were fed a regular diet. Platelet aggregation was enhanced significantly in normocalcemic VDRKO mice compared with wild type and hypocalcemic VDRKO mice. Aortic endothelial nitric-oxide (NO) synthase expression and urinary NOx excretions were reduced in hypocalcemic VDRKO mice, but not in normocalcemic VDRKO mice. Northern blot and RT-PCR analyses revealed that the gene expression of antithrombin in the liver as well as that of thrombomodulin in the aorta, liver and kidney was down-regulated in hypo- and normocalcemic VDRKO mice. Whereas tissue factor mRNA expression in the liver and kidney was up-regulated in VDRKO mice regardless of plasma calcium level. Furthermore, VDRKO mice manifested an exacerbated multi-organ thrombus formation after exogenous lipopolysaccharide injection regardless of the calcemic conditions. These results demonstrate that activation of nuclear VDR elicits antithrombotic effects in vivo, and suggest that the VDR system may play a physiological role in the maintenance of antithrombotic homeostasis.

Androgen Receptor Gene Knockout Male Mice Exhibit Impaired Cardiac Growth and Exacerbation of Angiotensin II-induced Cardiac Fibrosis

Androgen has anabolic effects on cardiac myocytes and has been shown to enhance left ventricular enlargement and function. However, the physiological and patho-physiological roles of androgen in cardiac growth and cardiac stress-induced remodeling remains unclear. We aimed to clarify whether the androgen-nuclear androgen receptor (AR) system contributes to the cardiac growth and angiotensin II (Ang II)-stimulated cardiac remodeling by using systemic AR-null male mice. AR knock-out (ARKO) male mice, at 25 weeks of age, and age-matched wild-type (WT) male mice were treated with or without Ang II stimulation (2.0 mg/kg/day) for 2 weeks. ARKO mice with or without Ang II stimulation showed a significant reduction in the heart-to-body weight ratio compared with those of WT mice. In addition, echocardiographic analysis demonstrated impairments of both the concentric hypertrophic response and left ventricular function in Ang II-stimulated ARKO mice. Western blot analysis of the myocardium revealed that activation of extracellular signal-regulated kinases (ERK) 1/2 and ERK5 by Ang II stimulation were lower in ARKO mice than those of WT mice. Ang II stimulation caused more prominent cardiac fibrosis in ARKO mice than in WT mice with enhanced expression of types I and III collagen and transforming growth factor-β1 genes and with increased Smad2 activation. These results suggest that, in male mice, the androgen-AR system participates in normal cardiac growth and modulates cardiac adaptive hypertrophy and fibrosis during the process of cardiac remodeling under hypertrophic stress.

Pitavastatin, an HMG-CoA Reductase Inhibitor, Exerts eNOS-Independent Protective Actions Against Angiotensin II–Induced Cardiovascular Remodeling and Renal Insufficiency

Angiotensin II (Ang II) plays a pivotal role in cardiovascular remodeling leading to hypertension, myocardial infarction, and stroke. Pitavastatin, an HMG-CoA reductase inihibitor, is known to have pleiotropic actions against the development of cardiovascular remodeling. The objectives of this study were to clarify the beneficial effects as well as the mechanism of action of pitavastatin against Ang II–induced organ damage. C57BL6/J mice at 10 weeks of age were infused with Ang II for 2 weeks and were simultaneously administered pitavastatin or a vehicle. Pitavastatin treatment improved Ang II–induced left ventricular hypertrophy and diastolic dysfunction and attenuated enhancement of cardiac fibrosis, cardiomyocyte hypertrophy, coronary perivascular fibrosis, and medial thickening. Ang II–induced oxidative stress, cardiac TGFβ-1 expression, and Smad 2/3 phosphorylation were all attenuated by pitavastatin treatment. Pitavastatin also reduced Ang II–induced cardiac remodeling and diastolic dysfunction in eNOS−/− mice as in wild-type mice. In eNOS−/− mice, the Ang II–induced cardiac oxidative stress and TGF-β–Smad 2/3 signaling pathway were enhanced, and pitavastatin treatment attenuated the enhanced oxidative stress and the signaling pathway. Moreover, pitavastatin treatment reduced the high mortality rate and improved renal insufficiency in Ang II–treated eNOS−/− mice, with suppression of glomerular oxidative stress and TGF-β-Smad 2/3 signaling pathway. In conclusion, pitavastatin exerts eNOS-independent protective actions against Ang II–induced cardiovascular remodeling and renal insufficiency through inhibition of the TGF-β-Smad 2/3 signaling pathway by suppression of oxidative stress.

Heparin Cofactor II Is a Novel Protective Factor Against Carotid Atherosclerosis in Elderly Individuals

Background—Thrombin plays a crucial role in atherothrombotic changes. Because heparin cofactor II (HCII) inhibits thrombin actions after binding to dermatan sulfate at injured arterial walls, HCII may negatively regulate thrombin actions in vascular walls. We hypothesized that plasma HCII activity is a preventive factor against atherosclerotic changes, especially in elderly individuals who already have atherosclerotic vascular injuries. Methods and Results—Maximum plaque thickness (MPT) in the carotid artery was measured by ultrasonography in 306 Japanese elderly individuals (154 men and 152 women; age, 40 to 91 years; 68.9±11.1 years, mean±SD). The relevance of cardiovascular risk factors including plasma HCII activity to the severity of MPT was statistically evaluated. Plasma HCII activity decreased with age. Simple linear regression analysis after adjustments for age and sex showed that lipoprotein(a), glycosylated hemoglobin A1c, and presence of diabetes mellitus significantly contributed to an increase in MPT values (r =0.119, P <0.05; r =0.196, P <0.001; and r =0.227, P <0.0001, respectively). In contrast, high-density lipoprotein (HDL) cholesterol and HCII activity were negatively correlated with MPT values (r =−0.117, P <0.05, and r =−0.202, P <0.0005, respectively). Multiple regression analysis revealed that plasma HCII activity and HDL cholesterol independently contributed to the suppression of MPT values and that the antiatherogenic contribution of HCII activity was stronger than that of HDL cholesterol (P <0.001 and P <0.05, respectively). Conclusions—These results suggest that HCII can be a novel and independent antiatherogenic factor. Moreover, HCII is a stronger predictive factor than HDL cholesterol against carotid atherosclerosis in elderly individuals.

High Plasma Heparin Cofactor II Activity Is Associated With Reduced Incidence of In-Stent Restenosis After Percutaneous Coronary Intervention

Background—Thrombin plays an important role in the development of atherosclerosis and restenosis after percutaneous coronary intervention. Because heparin cofactor II (HCII) inhibits thrombin action in the presence of dermatan sulfate, which is abundantly present in arterial wall, HCII may affect vascular remodeling by modulating thrombin action. We hypothesized that patients with high plasma HCII activity may show a reduced incidence of in-stent restenosis (ISR). Methods and Results—Sequential coronary arteries (n=166) with NIR stent (Boston Scientific Corp) implantation in 134 patients were evaluated before, immediately after, and at 6 months after percutaneous coronary intervention. Patients were divided into the following groups: high HCII (≥110%, 45 lesions in 36 patients), normal HCII (≥80% and <110%, 81 lesions in 66 patients), and low HCII (<80%, 40 lesions in 32 patients). Percent diameter stenosis at follow-up in the high-HCII group (18.7%) was significantly lower (P =0.046) than that in the normal-HCII group (30.3%) or the low-HCII group (29.0%). The ISR rate in the high-HCII group (6.7%) was significantly lower than that in the low-HCII group (30.0%) (P =0.0039). Furthermore, multivariate analysis demonstrated that high plasma HCII activity is an independent factor in reducing the incidence of angiographic restenosis (odds ratio, 0.953/1% increase of HCII; 95% CI, 0.911 to 0.998). Conclusions—The results demonstrate that HCII may have a hitherto unrecognized effect in inhibiting ISR. The effect of HCII may be mediated by inactivating thrombin in injured arteries, thereby inhibiting vascular smooth muscle cell migration and proliferation.

Chondromodulin I Is a Bone Remodeling Factor

ABSTRACT Chondromodulin I (ChM-I) was supposed from its limited expression in cartilage and its functions in cultured chondrocytes as a major regulator in cartilage development. Here, we generated mice deficient in ChM-I by targeted disruption of the ChM-I gene. No overt abnormality was detected in endochondral bone formation during embryogenesis and cartilage development during growth stages of ChM-I−/− mice. However, a significant increase in bone mineral density with lowered bone resorption with respect to formation was unexpectedly found in adult ChM-I−/− mice. Thus, the present study established that ChM-I is a bone remodeling factor.

Androgen-androgen receptor system protects against angiotensin II-induced vascular remodeling.

Age-related andropause promotes cardiovascular disease in males. Although we had previously reported that the androgen-androgen receptor (AR) system plays important roles in cardiac growth and remodeling, the systems involvement in vascular remodeling remains unclear. To clarify this role, 25-wk-old male AR knockout (ARKO) mice and littermate male wild-type (WT) mice were divided into two groups with and without angiotensin II (Ang II) administration (2.0 mg/kg . d) for 14 d, respectively. No morphological differences in the coronary artery and thoracic aorta were observed between the groups without Ang II. Ang II stimulation markedly increased medial thickness and perivascular fibrosis in ARKO mice, with enhanced TGF-beta1, collagen type I, and collagen type III gene expression in the aorta. Ang II stimulation also prominently increased superoxide production, lipid peroxidation, and gene expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase components in ARKO mice compared with WT mice. In addition, phosphorylation of c-Jun N-terminal kinase (JNK) and phosphorylated (Smad2/3) was remarkably enhanced in Ang II-treated ARKO mice compared with Ang II-treated WT mice. Notably, daily urinary nitric oxide (NO) metabolites excretion as a marker of NO bioavailability, aortic endothelial NO synthase expression and phosphorylation, and Akt phosphorylation were significantly reduced in ARKO mice compared with WT mice, regardless of Ang II stimulation. In conclusion, the androgen-AR system is required for the preservation of NO bioavailability through Akt-endothelial NO synthase system activation and exerts protective effects against Ang II-induced vascular remodeling by regulating oxidative stress, c-Jun N-terminal kinase (JNK) signaling, and the TGF-beta-phosphorylated Smad pathway.

Endothelial Nitric Oxide Synthase–Independent Protective Action of Statin Against Angiotensin II–Induced Atrial Remodeling via Reduced Oxidant Injury

Activation of the renin-angiotensin system exacerbates atrial remodeling, leading to atrial fibrillation and thrombosis, especially in a condition with decreased NO bioavailability. Recently, it has been reported that statins reduce the incidence of atrial fibrillation through attenuation of atrial remodeling; however, the mechanisms have not been completely elucidated. Therefore, we aimed to clarify the beneficial effect of statin on atrial remodeling in condition with reduced NO bioavailability. Endothelial NO synthase−/− mice were sham operated or infused with angiotensin II (Ang II) via an osmotic minipump for 2 weeks, and Ang II–infused mice were divided into 3 treatment groups: pitavastatin, Tempol (a free radical scavenger), or vehicle. Echocardiography and electrocardiography showed that Ang II infusion caused left atrial enlargement and a high incidence of atrial fibrillation, whereas pitavastatin and Tempol prevented these abnormalities. In histological analysis, Ang II–induced atrial interstitial fibrosis, perivascular fibrosis, and cardiomyocyte hypertrophy were all attenuated by pitavastatin and Tempol. Immunohistochemical staining showed that Ang II downregulated thrombomodulin and tissue factor pathway inhibitor and upregulated tissue factor and plasminogen activator inhibitor 1 in the left atrium and that pitavastatin and Tempol corrected the thrombogenic condition. Moreover, pitavastatin and Tempol reduced Ang II–induced atrial superoxide production and atrial transforming growth factor-&bgr;1 expression and Smad 2/3 phosphorylation. Atrial rac1-GTPase activity, known to activate NADPH oxidase, was attenuated by pitavastatin but not by Tempol. In conclusion, pitavastatin exerts endothelial NO synthase–independent protective actions against Ang II–induced atrial remodeling and atrial fibrillation with enhanced thrombogenicity through suppression of oxidant injury.

Strain-dependent embryonic lethality and exaggerated vascular remodeling in heparin cofactor II-deficient mice

Heparin cofactor II (HCII) specifically inhibits thrombin action at sites of injured arterial wall, and patients with HCII deficiency exhibit advanced atherosclerosis. However, the in vivo effects and the molecular mechanism underlying the action of HCII during vascular remodeling remain elusive. To clarify the role of HCII in vascular remodeling, we generated HCII-deficient mice by gene targeting. In contrast to a previous report, HCII(-/-) mice were embryonically lethal. In HCII(+/-) mice, prominent intimal hyperplasia with increased cellular proliferation was observed after tube cuff and wire vascular injury. The number of protease-activated receptor-1-positive (PAR-1-positive) cells was increased in the thickened vascular wall of HCII(+/-) mice, suggesting enhanced thrombin action in this region. Cuff injury also increased the expression levels of inflammatory cytokines and chemokines in the vascular wall of HCII(+/-) mice. The intimal hyperplasia in HCII(+/-) mice with vascular injury was abrogated by human HCII supplementation. Furthermore, HCII deficiency caused acceleration of aortic plaque formation with increased PAR-1 expression and oxidative stress in apoE-KO mice. These results demonstrate that HCII protects against thrombin-induced remodeling of an injured vascular wall by inhibiting thrombin action and suggest that HCII is potentially therapeutic against atherosclerosis without causing coagulatory disturbance.