Minoru Takaoka

Periadventitial Adipose Tissue Plays a Critical Role in Vascular Remodeling

Rationale: Obesity is associated with a high incidence of cardiovascular complications. However, the molecular link between obesity and vascular disease is not fully understood. Most previous studies have focused on the association between cardiovascular disease and accumulation of visceral fat. Periadventitial fat is distributed ubiquitously around arteries throughout the body. Objective: Here, we investigated the impact of obesity on inflammation in the periadventitial adipose tissue and on lesion formation after vascular injury. Methods and Results: High-fat, high-sucrose feeding induced inflammatory changes and decreased adiponectin expression in the periadventitial adipose tissue, which was associated with enhanced neointima formation after endovascular injury. Removal of periadventitial fat markedly enhanced neointima formation after injury, which was attenuated by transplantation of subcutaneous adipose tissue from mice fed on regular chow. Adiponectin-deficient mice showed markedly enhanced lesion formation, which was reversed by local delivery, but not systemic administration, of recombinant adiponectin to the periadventitial area. The conditioned medium from subcutaneous fat attenuated increased cell number of smooth muscle cells in response to platelet derived growth factor-BB. Conclusions: Our findings suggest that periadventitial fat may protect against neointimal formation after angioplasty under physiological conditions and that inflammatory changes in the periadventitial fat may have a direct role in the pathogenesis of vascular disease accelerated by obesity.

Endovascular Injury Induces Rapid Phenotypic Changes in Perivascular Adipose Tissue

Objective—Accumulating evidence suggests that adipose tissue not only stores energy but also secretes various bioactive substances called adipocytokines. Periadventitial fat is distributed ubiquitously around arteries throughout the body. It was reported that inflammatory changes in the periadventitial fat may have a direct role in the pathogenesis of vascular diseases accelerated by obesity. We investigated the effect of endovascular injury on the phenotype of perivascular fat. Methods and Results—Endovascular injury significantly upregulated proinflammatory adipocytokines and downregulated adiponectin within periadventitial fat tissue in models of mouse femoral artery wire injury and rat iliac artery balloon injury. Genetic disruption of tumor necrosis factor (TNF)-&agr; attenuated upregulation of proinflammatory adipocytokine expression, with reduced neointimal hyperplasia after vascular injury. Local delivery of TNF-&agr; to the periadventitial area enhanced inflammatory adipocytokine expression, which was associated with augmented neointimal hyperplasia in TNF-&agr;-deficient mice. Conditioned medium from a coculture of 3T3-L1 and RAW264 cells stimulated vascular smooth muscle cell proliferation. An anti-TNF-&agr; neutralizing antibody in the coculture abrogated the stimulating effect of the conditioned medium. Conclusion—Our findings indicate that endovascular injury induces rapid and marked changes in perivascular adipose tissue, mainly mediated by TNF-&agr;. It is suggested that the phenotypic changes in perivascular adipose tissue may have a role in the pathogenesis of neointimal hyperplasia after angioplasty.

Reciprocal expression of MRTF-A and myocardin is crucial for pathological vascular remodelling in mice

Myocardin‐related transcription factor (MRTF)‐A is a Rho signalling‐responsive co‐activator of serum response factor (SRF). Here, we show that induction of MRTF‐A expression is key to pathological vascular remodelling. MRTF‐A expression was significantly higher in the wire‐injured femoral arteries of wild‐type mice and in the atherosclerotic aortic tissues of ApoE−/− mice than in healthy control tissues, whereas myocardin expression was significantly lower. Both neointima formation in wire‐injured femoral arteries in MRTF‐A knockout (Mkl1−/−) mice and atherosclerotic lesions in Mkl1−/−; ApoE−/− mice were significantly attenuated. Expression of vinculin, matrix metallopeptidase 9 (MMP‐9) and integrin β1, three SRF targets and key regulators of cell migration, in injured arteries was significantly weaker in Mkl1−/− mice than in wild‐type mice. In cultured vascular smooth muscle cells (VSMCs), knocking down MRTF‐A reduced expression of these genes and significantly impaired cell migration. Underlying the increased MRTF‐A expression in dedifferentiated VSMCs was the downregulation of microRNA‐1. Moreover, the MRTF‐A inhibitor CCG1423 significantly reduced neointima formation following wire injury in mice. MRTF‐A could thus be a novel therapeutic target for the treatment of vascular diseases.

Inhibitory effect of efonidipine on aldosterone synthesis and secretion in human adrenocarcinoma (H295R) cells.

Targeting aldosterone synthesis and/or release represents a potentially useful approach to the prevention of cardiovascular disease. Aldosterone production is stimulated by angiotensin II (Ang II) or extracellular K+ and is mediated mainly by Ca2+ influx into adrenal glomerulosa cells through T-type calcium channels. We therefore examined the effects of efonidipine, a dual T-type/L-type Ca2+ channel blocker, on aldosterone secretion in the H295R human adrenocarcinoma cell line; 100 nmol/L Ang II and 10 mmol/L K+ respectively increased aldosterone secretion from H295R cells 12-fold and 9-fold over baseline. Efonidipine dose-dependently inhibited both Ang II- and K+-induced aldosterone secretion, and nifedipine, an L-type Ca2+ channel blocker, and mibefradil, a relatively selective T-type channel blocker, similarly inhibited Ang II- and K+-induced aldosterone secretion, but were much less potent than efonidipine. Efonidipine also lowered cortisol secretion most potently among these drugs. Notably, efonidipine and mibefradil also significantly suppressed Ang II- and K+-induced mRNA expression of 11-β-hydroxylase and aldosterone synthase, which catalyze the final two steps in the aldosterone synthesis, whereas nifedipine reduced only K+-induced enzyme expression. These findings suggest that efonidipine acts via T-type Ca2+ channel blockade to significantly reduce aldosterone secretion, and that this effect is mediated, at least in part, by suppression of 11-β-hydroxylase and aldosterone synthase expression.

The ATP-Binding Cassette Transporter BCRP1/ABCG2 Plays a Pivotal Role in Cardiac Repair After Myocardial Infarction Via Modulation of Microvascular Endothelial Cell Survival and Function

Objective—To clarify the impact of breast cancer resistance protein 1 (BCRP1)/ATP-binding cassette transporter subfamily G member 2 (ABCG2) expression on cardiac repair after myocardial infarction (MI). Methods and Results—The ATP-binding cassette transporter BCRP1/ABCG2 is expressed in various organs, including the heart, and may regulate several tissue defense mechanisms. BCRP1/ABCG2 was mainly expressed in endothelial cells of microvessels in the heart. MI was induced in 8- to 12-week-old wild-type (WT) and Bcrp1/Abcg2 knockout (KO) mice by ligating the left anterior descending artery. At 28 days after MI, the survival rate was significantly lower in KO mice than in WT mice because of cardiac rupture. Echocardiographic, hemodynamic, and histological assessments showed that ventricular remodeling was more deteriorated in KO than in WT mice. Capillary, myofibroblast, and macrophage densities in the peri-infarction area at 5 days after MI were significantly reduced in KO compared with WT mice. In vitro experiments demonstrated that inhibition of BCRP1/ABCG2 resulted in accumulation of intracellular protoporphyrin IX and impaired survival of microvascular endothelial cells under oxidative stress. Moreover, BCRP1/ABCG2 inhibition impaired migration and tube formation of endothelial cells. Conclusion—BCRP1/ABCG2 plays a pivotal role in cardiac repair after MI via modulation of microvascular endothelial cell survival and function.

Inflammatory Response to Acute Myocardial Infarction Augments Neointimal Hyperplasia After Vascular Injury in a Remote Artery

Objective—Percutaneous coronary intervention (PCI) is currently the most widely accepted treatment for acute myocardial infarction (AMI). It remains unclear, however, whether post-AMI conditions might exacerbate neointimal hyperplasia and restenosis following PCI. Given that both a medial smooth muscle cell lineage and a bone marrow (BM)-derived hematopoietic stem cell lineage are now thought to contribute to neointima formation, the primary aims of the present study were to determine whether AMI augments neointimal hyperplasia at sites of arterial injury, and whether BM-derived cells contribute to that process. Methods and Results—We simultaneously generated models of AMI and arterial injury in the same mice, some of which had received BM transplantation. We found that AMI augments neointimal hyperplasia at sites of femoral artery injury by ≈35% (P<0.05), but that while BM-derived cells contributed to neointimal hyperplasia, they did not contribute to the AMI-related augmentation. Expression of interleukin (IL)-6 mRNA was ≈7-fold higher in the neointimas of mice subjected to both AMI and arterial injury than in those of mice subjected to arterial injury alone. In addition, we observed increased synthesis of tumor necrosis factor (TNF)-&agr; within infarcted hearts and TNF-&agr; receptor type 1 (TNFR1) within injured arteries. Chronic treatment with pentoxifylline, which mainly inhibits TNF-&agr; synthesis, reduced levels of circulating TNF-&agr; and attenuated neointimal hyperplasia after AMI. Conclusions—Conditions after AMI could exacerbate postangioplasty restenosis, not by increasing mobilization of BM-derived cells, but by stimulating signaling via TNF-&agr;, TNFR1 and IL-6.

Aliskiren in combination with valsartan exerts synergistic protective effects against ventricular remodeling after myocardial infarction in mice

The efficacy of aliskiren, a direct renin inhibitor, in ventricular remodeling after myocardial infarction (MI) compared with conventional renin–angiotensin system (RAS) inhibitors remains to be defined. This study was performed to examine the protective effects of aliskiren and its addition to valsartan, an angiotensin-II receptor blocker, against ventricular remodeling after MI. MI was induced in 8- to 12-week-old C57BL/6 mice by ligating the left anterior descending artery. At 3 days after MI, mice were divided into five groups and were treated with the following: (1) phosphate-buffered saline (PBS); (2) hydralazine (10 mg kg–1 day–1); (3) valsartan (8 mg kg–1 day–1); (4) aliskiren (25 mg kg–1 day–1); and (5) combined aliskiren (25 mg kg–1 day–1) and valsartan (8 mg kg–1 day–1). With these doses of drugs, blood pressure-lowering effects compared with the PBS group were similar among the treated groups in sham-operated mice. At 28 days after MI, echocardiographic, hemodynamic and histological assessments demonstrated that monotherapy with valsartan or aliskiren alone significantly and similarly ameliorated ventricular remodeling after MI compared with the PBS and the hydralazine groups. Combination therapy of valsartan and aliskiren more greatly improved ventricular remodeling after MI with enhancement of angiogenesis and greater attenuation of tissue oxidative stress and inflammation. Our results indicate that aliskiren can be an alternative to conventional RAS inhibitors in the treatment of post-MI patients. Moreover, the dual therapy of valsartan and aliskiren may be more beneficial than either monotherapy. Further clinical trials will be warranted to sufficiently assess the safety and the efficacy of the use of aliskiren in post-MI patients.

The ATP-Binding Cassette Transporter ABCG2 Protects Against Pressure Overload–Induced Cardiac Hypertrophy and Heart Failure by Promoting Angiogenesis and Antioxidant Response

Objective—ATP-binding cassette transporter subfamily G member 2 (ABCG2), expressed in microvascular endothelial cells in the heart, has been suggested to regulate several tissue defense mechanisms. This study was performed to elucidate its role in pressure overload–induced cardiac hypertrophy. Methods and Results—Pressure overload was induced in 8- to 12-week-old wild-type and Abcg2−/− mice by transverse aortic constriction (TAC). Abcg2−/− mice showed exaggerated cardiac hypertrophy and ventricular remodeling after TAC compared with wild-type mice. In the early phase after TAC, functional impairment in angiogenesis and antioxidant response in myocardium was found in Abcg2−/− mice. In vitro experiments demonstrated that ABCG2 regulates transport of glutathione, an important endogenous antioxidant, from microvascular endothelial cells. Besides, glutathione transported from microvascular endothelial cells in ABCG2-dependent manner ameliorated oxidative stress–induced cardiomyocyte hypertrophy. In vivo, glutathione levels in plasma and the heart were increased in wild-type mice but not in Abcg2−/− mice after TAC. Treatment with the superoxide dismutase mimetic ameliorated cardiac hypertrophy in Abcg2−/− mice after TAC to the same extent as that in wild-type mice, although cardiac dysfunction with impaired angiogenesis was observed in Abcg2−/− mice. Conclusion—ABCG2 protects against pressure overload–induced cardiac hypertrophy and heart failure by promoting angiogenesis and antioxidant response.

Unique remodeling processes after vascular injury in intracranial arteries: analysis using a novel mouse model

The effectiveness of angioplasty and stenting in intracranial atherosclerotic diseases is controversial due to high rates of delayed restenosis and hemorrhage compared with extracranial arteries. However, the mechanisms underlying these differences are still unclear, because their pathophysiology is yet to be examined. To address this issue, we established a novel vascular injury model in the intracranial internal carotid arteries (IICAs) in mice, and analyzed the remodeling process in comparison to that of the femoral arteries (FAs). In IICAs, neointimal hyperplasia was observed from day 14 and grew until day 56. Although smooth muscle cells (SMCs) emerged in the neointima from day 28, SMCs in the injured media were continuously lost with eventual extinction of the media. Re-endothelialization was started from day 7 and completed on day 28. Accumulation of macrophages was continued in the adventitia until day 56. Compared with FAs, the following points are unique in IICAs: (1) delayed continuous formation of neointima; (2) accumulation of macrophages in the media on day 14;(3) continuous loss of SMCs in the media followed by extinction of the media itself; and (4) continuously growing adventitia. These pathophysiologic differences might be associated with unfavorable outcomes in percutaneous transluminal angioplasty and stenting in intracranial arteries.