Mitsuhisa Koga

Pressure-independent effects of angiotensin II on hypertensive myocardial fibrosis.

Abstract—Angiotensin II (Ang II) is implicated in the proinflammatory process in various disease situations. Thus, we sought to determine the role of Ang II in early inflammation-induced fibrosis of pressure-overloaded (PO) hearts. PO was induced by suprarenal aortic constriction (AC) at day 0 in male Wistar rats, and they were orally administered 0.1 mg/kg per day candesartan every day from day −7. This was the maximum dose of candesartan that did not change arterial pressure in hypertensive rats with AC (AC rats). In AC rats, cardiac angiotensin-converting enzyme (ACE) activity was transiently enhanced after day 1 and peaked at day 3, declining to lower levels by day 14, whereas serum ACE activity was not changed. In AC rats, PO induced early fibroinflammatory changes (monocyte chemoattractant factor [MCP]-1 and transforming growth factor [TGF]-&bgr; expression, perivascular macrophage accumulation, and fibroblast proliferation), and thereafter, left ventricular hypertrophy developed, featuring myocyte hypertrophy, intramyocardial arterial wall thickening, and perivascular and interstitial fibroses. Candesartan suppressed the induction of MCP-1 and TGF-&bgr; and reduced macrophage accumulation and fibroblast proliferation in PO hearts. Candesartan significantly prevented perivascular and interstitial fibrosis. However, candesartan did not affect myocyte hypertrophy and arterial wall thickening. In conclusion, a subdepressor dose of candesartan prevented the MCP-1–mediated inflammatory process and reactive myocardial fibrosis in PO hearts. Ang II might play a key role in reactive fibrosis in hypertensive hearts, independent of arterial pressure changes.

Brain pericytes among cells constituting the blood-brain barrier are highly sensitive to tumor necrosis factor-α, releasing matrix metalloproteinase-9 and migrating in vitro

BackgroundIncreased matrix metalloproteinase (MMP)-9 in the plasma and brain is associated with blood-brain barrier (BBB) disruption through proteolytic activity in neuroinflammatory diseases. MMP-9 is present in the brain microvasculature and its vicinity, where brain microvascular endothelial cells (BMECs), pericytes and astrocytes constitute the BBB. Little is known about the cellular source and role of MMP-9 at the BBB. Here, we examined the ability of pericytes to release MMP-9 and migrate in response to inflammatory mediators in comparison with BMECs and astrocytes, using primary cultures isolated from rat brains.MethodsThe culture supernatants were collected from primary cultures of rat brain endothelial cells, pericytes, or astrocytes. MMP-9 activities and levels in the supernatants were measured by gelatin zymography and western blot, respectively. The involvement of signaling molecules including mitogen-activated protein kinases (MAPKs) and phosphoinositide-3-kinase (PI3K)/Akt in the mediation of tumor necrosis factor (TNF)-α-induced MMP-9 release was examined using specific inhibitors. The functional activity of MMP-9 was evaluated by a cell migration assay.ResultsZymographic and western blot analyses demonstrated that TNF-α stimulated pericytes to release MMP-9, and this release was much higher than from BMECs or astrocytes. Other inflammatory mediators [interleukin (IL)-1β, interferon-γ, IL-6 and lipopolysaccharide] failed to induce MMP-9 release from pericytes. TNF-α-induced MMP-9 release from pericytes was found to be mediated by MAPKs and PI3K. Scratch wound healing assay showed that in contrast to BMECs and astrocytes the extent of pericyte migration was significantly increased by TNF-α. This pericyte migration was inhibited by anti-MMP-9 antibody.ConclusionThese findings suggest that pericytes are most sensitive to TNF-α in terms of MMP-9 release, and are the major source of MMP-9 at the BBB. This pericyte-derived MMP-9 initiated cellular migration of pericytes, which might be involved in pericyte loss in the damaged BBB.

Inhibition of Progression and Stabilization of Plaques by Postnatal Interferon-γ Function Blocking in ApoE-Knockout Mice

A role of interferon-γ is suggested in early development of atherosclerosis. However, the role of interferon-γ in progression and destabilization of advanced atherosclerotic plaques remains unknown. Thus, the aim of this study was to determine whether postnatal inhibition of interferon-γ signaling could inhibit progression of atherosclerotic plaques and stabilize the lipid- and macrophage-rich advanced plaques. Atherosclerotic plaques were induced in ApoE-knockout (KO) mice by feeding high-fat diet from 8 weeks old (w). Interferon-γ function was postnatally inhibited by repeated gene transfers of a soluble mutant of interferon-γ receptors (sIFNγR), an interferon-γ inhibitory protein, into the thigh muscle every 2 weeks. When sIFNγR treatment was started at 12 w (atherosclerotic stage), sIFNγR not only prevented plaque progression but also stabilized advanced plaques at 16 w: sIFNγR decreased accumulations of the lipid and macrophages and increased fibrotic area with more smooth muscle cells. Moreover, sIFNγR downregulated expressions of proinflammatory cytokines, chemokines, adhesion molecules, and matrix metalloproteinases but upregulated procollagen type I. sIFNγR did not affect serum cholesterol levels. In conclusion, postnatal blocking of interferon-γ function by sIFNγR treatment would be a new strategy to inhibit plaque progression and to stabilize advanced plaques through the antiinflammatory effects.

Roles of Intercellular Adhesion Molecule-1 in Hypertensive Cardiac Remodeling

Abstract—Recently, we have shown that in rats with a suprarenal abdominal aortic constriction (AC), pressure overload induces early perivascular fibro-inflammatory changes (transforming growth factor [TGF]-&bgr; induction and fibroblast proliferation) within the first week after AC and then causes the development of cardiac remodeling (myocyte hypertrophy and reactive myocardial fibrosis) associated with diastolic dysfunction. Intercellular adhesion molecule (ICAM)-1 is implicated in the recruitment of leukocytes, especially macrophages, in various inflammatory situations. Thus, we sought to investigate the causal relation of ICAM-1 to macrophage recruitment and cardiac remodeling in AC rats. In AC rats, immunoreactive ICAM-1 was observed transiently on endothelial cells of the intramyocardial coronary arterioles after day 1, with a peak at day 3, returning to baseline by day 7. Also, ED1+ macrophage accumulation was found in the area adjacent to the arteries expressing ICAM-1. Chronic treatment with an anti–ICAM-1 neutralizing antibody, but not with control IgG, remarkably reduced the accumulations of macrophages and proliferative fibroblasts and inhibited the upregulation of TGF-&bgr; expression. Furthermore, the neutralizing antibody significantly prevented myocardial fibrosis without affecting arterial pressure and left ventricular and myocyte hypertrophy. In conclusion, ICAM-1 expression was induced by pressure overload in the intramyocardial arterioles, and triggered perivascular macrophage accumulation. In pressure-overloaded hearts, a crucial role in ICAM-1–mediated macrophage accumulation was suggested in the development of myocardial fibrosis, through TGF-&bgr; induction and fibroblast activation.

Exaggerated Blood Pressure Variability Superimposed on Hypertension Aggravates Cardiac Remodeling in Rats via Angiotensin II System-Mediated Chronic Inflammation

Hypertensive patients with large blood pressure variability (BPV) have aggravated end-organ damage. However, the pathogenesis remains unknown. We investigated whether exaggerated BPV aggravates hypertensive cardiac remodeling and function by activating inflammation and angiotensin II–mediated mechanisms. A model of exaggerated BPV superimposed on chronic hypertension was created by performing bilateral sinoaortic denervation (SAD) in spontaneously hypertensive rats (SHRs). SAD increased BPV to a similar extent in Wistar Kyoto rats and SHRs without significant changes in mean blood pressure. SAD aggravated left ventricular and myocyte hypertrophy and myocardial fibrosis to a greater extent and impaired left ventricular systolic function in SHRs. SAD induced monocyte chemoattractant protein-1, transforming growth factor-&bgr;, and angiotensinogen mRNA upregulations and macrophage infiltration of the heart in SHRs. The effects of SAD on cardiac remodeling and inflammation were much smaller in Wistar Kyoto rats compared with SHRs. Circulating levels of norepinephrine, the active form of renin, and inflammatory cytokines were not affected by SAD in Wistar Kyoto rats and SHRs. A subdepressor dose of candesartan abolished the SAD-induced left ventricular/myocyte hypertrophy, myocardial fibrosis, macrophage infiltration, and inductions of monocyte chemoattractant protein-1, transforming growth factor-&bgr;, and angiotensinogen and subsequently prevented systolic dysfunction in SHRs with SAD. These findings suggest that exaggerated BPV induces chronic myocardial inflammation and thereby aggravates cardiac remodeling and systolic function in hypertensive hearts. The cardiac angiotensin II system may play a role in the pathogenesis of cardiac remodeling and dysfunction induced by a combination of hypertension and exaggerated BPV.

Oncostatin M, an Interleukin-6 Family Cytokine, Upregulates Matrix Metalloproteinase-9 Through the Mitogen-Activated Protein Kinase Kinase-Extracellular Signal-Regulated Kinase Pathway in Cultured Smooth Muscle Cells

Objectives—Matrix metalloproteinase (MMP)-9 is implicated in extracellular matrix (ECM) degradation of atherosclerotic lesions. Oncostatin M (OSM) regulates ECM metabolism in various kinds of cells. Thus, we sought to investigate whether OSM regulates MMP-9 expression in cultured rat aortic smooth muscle cells (SMCs) and, if so, to determine the signaling pathway for MMP-9 induction by OSM. Methods and Results—Competitive reverse transcriptase polymerase chain reaction showed that OSM upregulated MMP-9 mRNA expression, peaking at 4 hours and returning to unstimulated levels by 24 hours. Gelatin zymography revealed that MMP-9 activity was increased in the conditioned medium after the 24-hour OSM treatment. Immunoblot analysis demonstrated that OSM transiently induced extracellular signal-regulated kinase (ERK)1/2 and STAT3 phosphorylations with a peak at 15 and 5 minutes, respectively. A MEK1 inhibitor, PD98059, not only blocked ERK1/2 phosphorylation but also abolished the OSM-induced MMP-9 upregulation, whereas the MMP-9 induction was not affected by overexpressing dominant-negative STAT3. In addition, OSM slightly upregulated MMP-2 and downregulated tissue inhibitors of MMP-1 and -3 through different mechanisms from that in case of MMP-9. Conclusions—OSM upregulates MMP-9 expression in SMCs through the MEK-ERK but not STAT3 pathway.

Rho-kinase inhibition reduces neointima formation after vascular injury by enhancing Bax expression and apoptosis.

Summary: Recently, we have shown that a specific Rho‐kinase inhibitor, Y27632 (R‐(+)‐trans‐N‐(4‐pyridyl)‐4‐(1‐aminoethyl)‐ cyclohexanecarboxamide), prevents neointima formation after vascular injury associated with increased terminal deoxynucleotidyl transferase‐mediated dUTP nickend labeling (TUNEL)+ smooth muscle cells. Because the mechanism of the action of Y27632 remains unclear, we investigated the expression changes in Bcl family proteins, apoptosis regulators of smooth muscle cells, in the rat carotid artery after balloon injury (BI). Y27632 (BI + Y group) or saline (BI group) was administered peritoneally from Day 1 to Day 14 after BI. Y27632 markedly prevented neointima formation at Day 14. In the BI group, TUNEL+ smooth muscle cells were transiently increased in the neointima, but not in the media, with a peak at Day 7, returning to a lower level by Day 14. Y27632 significantly increased TUNEL+ smooth muscle cells at Days 7 and 14. Smooth muscle cell apoptosis was confirmed by electron microscopic examination. At Day 14, although proapoptotic Bax was slightly, but not significantly, increased in the BI group, it was significantly upregulated in the BI + Y group. Antiapoptotic Bcl‐xL was upregulated in the BI group, and the upregulated Bcl‐xL was not affected by Y27632. These findings indicate that Rho‐kinase inhibition induces neointimal smooth muscle cell apoptosis through Bax upregulation, resulting in reduced neointima formation.

Inhibition of Intrinsic Interferon-γ Function Prevents Neointima Formation After Balloon Injury

It is still controversial whether intrinsic interferon (IFN)-&ggr; promotes or attenuates vascular remodeling in hyperproliferative vascular disorders, such as neointima formation after balloon injury. Thus, we investigated whether inhibition of intrinsic IFN-&ggr; function prevents neointima formation. For this purpose, naked DNA plasmid encoding a soluble mutant of IFN-&ggr; receptor &agr;-subunit (sIFN&ggr;R; an IFN-&ggr; inhibitory protein) or mock plasmid was injected into the thigh muscle of male Wistar rats 2 days before balloon injury (day −2). sIFN&ggr;R gene transfer significantly elevated serum levels of sIFN&ggr;R protein for 2 weeks. In mock-treated rats, balloon injury induced smooth muscle cell proliferation in the neointima with a peak at day 7 and produced thick neointima at day 14. sIFN&ggr;R treatment reduced the number of proliferating intimal smooth muscle cells by 50% at day 7 and attenuated neointima formation with a 45% reduction of the intima/media area ratio at day 14. In mock-treated rats, at day 7, balloon injury induced phosphorylation of signal transducer and activator of transcription-1 and upregulations of IFN regulatory factor-1 (a transcription factor mediating IFN-&ggr; signal). Balloon injury also upregulated the key molecules of neointima formation, such as intercellular adhesion molecule-1 and platelet-derived growth factor &bgr;-receptor. These changes were suppressed by sIFN&ggr;R treatment. In conclusion, it is suggested that intrinsic IFN-&ggr; promotes neointima formation probably through IFN regulatory factor-1/intercellular adhesion molecule-1–mediated and platelet-derived growth factor–mediated mechanisms. Thus, inhibition of IFN-&ggr; signaling may be a new therapeutic target for prevention of neointima formation of hyperproliferative vascular disorders.

Simvastatin prevents large blood pressure variability induced aggravation of cardiac hypertrophy in hypertensive rats by inhibiting RhoA/Ras-ERK pathways.

Pronounced variability in blood pressure (BP) is an aggravating factor of hypertensive end-organ damage. However, its pathogenesis remains unknown. Statins have various protective effects on the cardiovascular system. Thus, we determined whether simvastatin would attenuate the aggravation of hypertensive cardiac remodeling in a rat model of hypertension with large BP variability, and also investigated the signaling mechanism involved in its effect. A model of hypertension with large BP variability was created by performing bilateral sinoaortic denervation (SAD) in spontaneously hypertensive rats (SHRs). A SAD or sham operation was performed in 12-week-old rats. Thereafter, simvastatin (0.2 mg kg−1 per day) or vehicle was intraperitoneally administered every day. After 6 weeks , telemetric recordings revealed that SAD enhanced BP variability without changing the mean BP. SAD increased myocyte hypertrophy, myocardial fibrosis and macrophage infiltration associated with the upregulation of brain natriuretic peptide (BNP), type I procollagen, transforming growth factor (TGF)-β and monocyte chemoattractant protein (MCP)-1, and activation of RhoA, Ras and ERK1/2. Simvastatin did not change the mean BP or BP variability in SAD-operated SHRs. In SAD-operated SHRs, simvastatin attenuated myocyte hypertrophy and BNP expression, as well as RhoA, Ras and ERK1/2 activities. In contrast, simvastatin did not change myocardial fibrosis, macrophage infiltration, or the expression of procollagen and TGF-β or MCP-1 in SAD-operated SHRs. Simvastatin did not affect serum lipid levels. In conclusion, simvastatin attenuated the large BP variability-induced aggravation of cardiac hypertrophy, but not myocardial fibrosis, in SHRs. The activation of RhoA/Ras–ERK pathways may contribute to the aggravation of cardiac hypertrophy by a combination of hypertension and large BP variability.

Enhanced cardiac inflammation and fibrosis in ovariectomized hypertensive rats: a possible mechanism of diastolic dysfunction in postmenopausal women.

Diastolic dysfunction is more prevalent in individuals with hypertension, particularly postmenopausal women; however, the pathogenesis of diastolic dysfunction remains unknown. Pressure overload activates cardiac inflammation, which induces myocardial fibrosis and diastolic dysfunction in rats with a suprarenal aortic constriction (AC). Therefore, we examined the effects of bilateral ovariectomy (OVX) on left ventricle (LV) remodeling, diastolic dysfunction and cardiac inflammation in hypertensive female rats. Rats were randomized to OVX+AC, OVX and AC groups as well as a Control group receiving sham operations for both the procedures. Rats underwent OVX at 6 weeks and AC at 10 weeks (Day 0). At Day 28, OVX did not appear to affect arterial pressure, cardiac hypertrophy or LV fractional shortening in AC rats. However, OVX increased myocardial fibrosis, elevated LV end-diastolic pressure and reduced the transmitral Doppler spectra early to late filling velocity ratio in AC rats. AC-induced transient myocardial monocyte chemoattractant protein-1 expression and macrophage infiltration, both of which peaked at Day 3 and were augmented and prolonged by OVX. At Day 28, dihydroethidium staining revealed superoxide generation in the intramyocardial arterioles in the OVX+AC group but not in the AC group. NOX1, a functional subunit of nicotinamide adenine dinucleotide phosphate oxidase, was upregulated only in the OVX+AC group at Day 28. Chronic 17β-estradiol replacement prevented the increases in macrophage infiltration, NOX1 upregulation, myocardial fibrosis and diastolic dysfunction in OVX+AC rats. In conclusion, we suggest that estrogen deficiency augments cardiac inflammation and oxidative stress and thereby aggravates myocardial fibrosis and diastolic dysfunction in hypertensive female rats. The findings provide insight into the mechanism underlying diastolic dysfunction in hypertensive postmenopausal women.