Biomedical subjects

Mika Laine

Publications and source records attributed to Mika Laine.

9 recordsLinked to original sources

PubMed2006

Mast cell chymase induces smooth muscle cell apoptosis by disrupting NF-kappaB-mediated survival signaling.

Chymase released from activated mast cells induces apoptosis of vascular smooth muscle cells (SMCs) in vitro by degrading the pericellular matrix component fibronectin, so causing disruption of focal adhesion complexes and Akt dephosphorylation, which are necessary for cell adhesion and survival. However, the molecular mechanisms of chymase-mediated apoptosis downstream of Akt have remained elusive. Here, we show by means of RT-PCR, Western blotting, EMSA, immunocytochemistry and confocal microscopy, that chymase induces SMC apoptosis by disrupting NF-kappaB-mediated survival signaling. Following chymase treatment, the translocation of active NF-kappaB/p65 to the nucleus was partly abolished and the amount of nuclear p65 was reduced. Pretreatment of SMCs with chymase also inhibited LPS- and IL-1beta-induced nuclear translocation of p65. The chymase-induced degradation of p65 was mediated by active caspases. Loss of NF-kappaB-mediated transactivation resulted in downregulation of bcl-2 mRNA and protein expression, leading to mitochondrial swelling and release of cytochrome c. The apoptotic process involved activation of both caspase 9 and caspase 8. The results reveal that, by disrupting the NF-kappaB-mediated survival-signaling pathway, activated chymase-secreting mast cells can mediate apoptosis of cultured arterial SMCs. Since activated mast cells colocalize with apoptotic SMCs in vulnerable areas of human atherosclerotic plaques, they may participate in the weakening and rupture of atherosclerotic plaques.

Active Transport, Cell Nucleus↗

PubMed2006

Possible role for mast cell-derived cathepsin G in the adverse remodelling of stenotic aortic valves.

AIMS: Aortic stenosis (AS) is characterized by extensive remodelling of the valves, including infiltration of inflammatory cells, extracellular matrix degradation, and fibrosis. The molecular mechanisms behind this adverse remodelling have remained obscure. In this article, we study whether cathepsin G, an angiotensin II (Ang II)-forming elastolytic enzyme, contributes to progression of AS. METHODS AND RESULTS: Stenotic aortic valves (n = 86) and control valves (n = 17) were analysed for cathepsin G, transforming growth factor-beta1 (TGF-beta1), and collagens I and III with RT-PCR and immunohistochemistry. Valvular collagen/elastin ratio was quantified by histochemistry. In stenotic valves, cathepsin G was present in mast cells and showed increased expression (P < 0.001), which correlated positively (P < 0.001) with the expression levels of TGF-beta1 and collagens I and III. TGF-beta1 was also present in mast cell-rich areas and cathepsin G induced losartan-sensitive TGF-beta1 expression in cultured fibroblasts. Collagen/elastin ratio was increased in stenotic valves (P < 0.001) and correlated positively with smoking (P = 0.02). Nicotine in cigarette smoke activated mast cells and induced TGF-beta1 expression in cultured fibroblasts. Fragmented elastin was observed in stenotic valves containing activated cathepsin G-secreting mast cells and in normal valves treated with cathepsin G. CONCLUSION: In stenotic aortic valves, mast cell-derived cathepsin G may cause adverse valve remodelling and AS progression.

Adult↗

PubMed2006

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Journal Article↗

PubMed2005

Downregulation of the HERG (KCNH2) K(+) channel by ceramide: evidence for ubiquitin-mediated lysosomal degradation.

The HERG (KCNH2) potassium channel underlies the rapid component of the delayed rectifier current (I(kr)), a current contributing to the repolarisation of the cardiac action potential. Mutations in HERG can cause the hereditary forms of the short-QT and long-QT syndromes, predisposing to ventricular arrhythmias and sudden cardiac death. HERG is expressed mainly in the cell membrane of cardiac myocytes, but has also been identified in cell membranes of a range of other cells, including smooth muscle and neurones. The mechanisms regulating the surface expression have however not yet been elucidated. Here we show, using stable HERG-expressing HEK 293 cells, that ceramide evokes a time-dependent decrease in HERG current which was not attributable to a change in gating properties of the channel. Surface expression of the HERG channel protein was reduced by ceramide as shown by biotinylation of surface proteins, western blotting and immunocytochemistry. The rapid decline in HERG protein after ceramide stimulation was due to protein ubiquitylation and its association with lysosomes. The results demonstrate that the surface expression of HERG is strictly regulated, and that ceramide modifies HERG currents and targets the protein for lysosomal degradation.

Cells, Cultured↗

PubMed2005

Vasopeptidase inhibition has beneficial cardiac effects in spontaneously diabetic Goto-Kakizaki rats.

In this study we examined diabetes- and hypertension-induced changes in cardiac structure and function in an animal model of type 2 diabetes, the Goto-Kakizaki (GK) rat. We hypothesized that treatment with omapatrilat, a vasopeptidase inhibitor, which causes simultaneous inhibition of angiotensin converting enzyme and neutral endopeptidase, provides additional cardioprotective effects, during normal- as well as high sodium intake, compared to treatment with enalapril, a selective inhibitor of angiotensin converting enzyme. Fifty-two GK rats were randomized into 6 groups to receive either normal-sodium (NaCl 0.8%) or high-sodium (NaCl 6%) diet and enalapril, omapatrilat or vehicle for 12 weeks. The GK rats developed hypertension, cardiac hypertrophy and overexpression of cardiac natriuretic peptides and profibrotic connective tissue growth factor compared to nondiabetic Wistar rats. The high dietary sodium further increased the systolic blood pressure, and changed the mitral inflow pattern measured by echocardiography towards diastolic dysfunction. Enalapril and omapatrilat equally decreased the systolic blood pressure compared to the control group during normal- as well as high-sodium diet. Both drugs had beneficial cardioprotective effects, which were blunted by the high dietary sodium. Compared to enalapril, omapatrilat reduced the echocardiographically measured left ventricular mass during normal-sodium diet and improved the diastolic function during high-sodium diet in GK rats. Furthermore, omapatrilat reduced relative cardiac weight more effectively than enalapril during high sodium intake. Our results suggest that both the renin-angiotensin and the neutral endopeptidase system are involved in the pathogenesis of diabetic cardiomyopathy since vasopeptidase inhibition was shown to provide additional benefits in comparison with selective angiotensin converting enzyme inhibition alone.

Aldosterone↗

PubMed2004

Induction of local angiotensin II-producing systems in stenotic aortic valves.

OBJECTIVES: The purpose of this study was to investigate the expression of angiotensin II (Ang II)-producing enzyme systems in normal and stenotic aortic valves. BACKGROUND: Chronic inflammation and fibrosis are involved in the pathogenesis of aortic stenosis (AS), but the detailed molecular mechanisms of this atherosclerosis-like process remain obscure. Angiotensin II, a powerful mediator of inflammation and fibrosis, may participate in AS progression. METHODS: Stenotic aortic valves (n = 86) were obtained from patients undergoing valve replacement surgery, and control valves (n = 11) were obtained from patients undergoing cardiac transplantation. Angiotensin-converting enzyme (ACE) and mast cell (MC)-derived chymase were quantified by reverse-transcription polymerase chain reaction, autoradiography, and immunostaining. The MCs, macrophages, and T lymphocytes were detected by immunohistochemistry, and angiotensin II type 1 receptor (AT-1R) by autoradiography. RESULTS: Compared with control valves, stenotic aortic valves showed a significant increase in both messenger ribonucleic acid (mRNA) (p = 0.001) and protein (p < 0.001) expression of ACE, which colocalized with macrophages. Similarly, the expression of AT-1R protein and chymase mRNA and protein was upregulated (p < 0.001), and the number of MCs was six-fold higher in stenotic than in normal valves. The MCs were associated with the calcified areas, and-in contrast to control valves-showed an increased degree of degranulation, a prerequisite for chymase secretion and action. CONCLUSIONS: Angiotensin-converting enzyme and chymase, two Ang II-forming enzymes, are locally expressed in aortic valves, and owing to infiltration of macrophages and MCs, are further upregulated in stenotic valves. These novel findings, implicating chronic inflammation and an increased expression of local Ang II-forming systems, suggest that therapeutic interventions aiming at inhibiting these processes may slow AS progression.

Adult↗

PubMed2004

Cardioprotective effects of vasopeptidase inhibition vs. angiotensin type 1-receptor blockade in spontaneously hypertensive rats on a high salt diet.

The aim of our study was to compare the cardioprotective effects of vasopeptidase inhibition with those of angiotensin type 1 (AT1)-receptor blockade, a diuretic and the combination of AT1-receptor blockade and a diuretic in an experimental rat model of essential hypertension on a high salt diet. Spontaneously hypertensive rats (SHR) (n =73) were divided into 6 groups to receive the following diet and drug regimens for 8 weeks: 1) low salt controls (NaCl 0.5%); 2) high salt controls (NaCl 6%); 3) omapatrilat (40 mg/kg/d) on a high salt diet; 4) losartan (30 mg/kg/d) on a high salt diet; 5) hydrochlorothiazide (HCTZ; 10 mg/kg/d) on a high salt diet; and 6) losartan+HCTZ (30+10 mg/kg/d) on a high salt diet. Blood pressure was measured by tail-cuff plethysmography. The histological score of myocardial damage, myocardial collagen volume fraction (CVF), connective tissue growth factor (CTGF) expression and cardiomyocyte apoptosis were determined. As an antihypertensive, omapatrilat showed greater efficacy than monotherapy with losartan or HCTZ, and was equally effective as the combination of losartan+HCTZ. Assessed by myocardial damage score, omapatrilat and losartan protected cardiac morphology better than HCTZ or the drug combination. Omapatrilat decreased CVF to a greater extent than the other therapies, whereas losartan was most effective in decreasing CTGF expression. All drug treatments, except HCTZ, decreased cardiomyocyte apoptosis. Our findings provide evidence that both vasopeptidase inhibition and AT1-receptor blockade exert cardioprotective properties beyond their blood pressure-lowering effects. Cardioprotection was associated with prevention of cardiomyocyte apoptosis and inhibition of extracellular matrix formation.

Aldosterone↗

PubMed2003

Effect of vasopeptidase inhibitor omapatrilat on cardiomyocyte apoptosis and ventricular remodeling in rat myocardial infarction.

We have shown earlier that cardiomyocyte apoptosis continues at a high level late after myocardial infarction and contributes to adverse cardiac remodeling. Here we studied whether this process can be inhibited by the vasopeptidase inhibitor omapatrilat, a drug which causes simultaneous inhibition of both angiotensin converting enzyme and neutral endopeptidase. Our hypothesis was that omapatrilat-treated rats would have less cardiomyocyte apoptosis, and less adverse cardiac remodeling compared to rats treated with selective inhibitors of angiotensin converting enzyme, neutral endopeptidase or placebo. Myocardial infarction was produced by ligation of the left anterior descending coronary artery. Rats were randomized to receive omapatrilat, captopril, neutral endopeptidase inhibitor SQ-28603 or vehicle. Rats treated with omapatrilat and captopril had reduced cardiac BNP mRNA levels and less myocardial fibrosis by comparison with the vehicle-treated rats. However, omapatrilat was more effective than captopril in attenuating hypertrophy as measured by relative cardiac weight (3.0+/-0.2 vs. 3.8+/-0.2 mg/g, P<0.01) or by echocardiographically determined left ventricular mass (0.61+/-0.05 vs. 0.83+/-0.06 g, P<0.01). Myocardial apoptosis was elevated both in the infarction border zone (0.129+/-0.017%) and in the remote area (0.035+/-0.005%) still 4 weeks after myocardial infarction. Angiotensin converting enzyme inhibition proved to be important in the prevention of apoptosis since both omapatrilat and captopril reduced the number of apoptotic myocytes whereas selective neutral endopeptidase inhibitor SQ-28603 had no effect. In conclusion, myocardial apoptosis, remaining increased 4 weeks after myocardial infarction, was reduced by angiotensin converting enzyme inhibition. Vasopeptidase inhibition was more effective than selective angiotensin converting enzyme inhibition in preventing adverse cardiac remodeling after myocardial infarction.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2002

The role of inositol 1,4,5-trisphosphate receptors in Ca(2+) signalling and the generation of arrhythmias in rat atrial myocytes.

Various cardio-active stimuli, including endothelin-1 (ET-1), exhibit potent arrhythmogenicity, but the underlying cellular mechanisms of their actions are largely unclear. We used isolated rat atrial myocytes and related changes in their subcellular Ca(2+) signalling to the ability of various stimuli to induce diastolic, premature extra Ca(2+) transients (ECTs). For this, we recorded global and spatially resolved Ca(2+) signals in indo-1- and fluo-4-loaded atrial myocytes during electrical pacing. ET-1 exhibited a higher arrhythmogenicity (arrhythmogenic index; ratio of number of ECTs over fold-increase in Ca(2+) response, 8.60; n = 8 cells) when compared with concentrations of cardiac glycosides (arrhythmogenic index, 4.10; n = 8 cells) or the beta-adrenergic agonist isoproterenol (arrhythmogenic index, 0.11; n = 6 cells) that gave similar increases in the global Ca(2+) responses. Seventy-five percent of the ET-1-induced arrhythmogenic Ca(2+) transients were accompanied by premature action potentials, while for digoxin this proportion was 25 %. The beta-adrenergic agonist failed to elicit a significant number of ECTs. Direct activation of inositol 1,4,5-trisphosphate (InsP(3)) receptors with a membrane-permeable InsP(3) ester (InsP(3) BM) mimicked the effect of ET-1 (arrhythmogenic index, 14.70; n = 6 cells). Inhibition of InsP(3) receptors using 2 microM 2-aminoethoxydiphenyl borate, which did not display any effects on Ca(2+) signalling under control conditions, specifically suppressed the arrhythmogenic action of ET-1 and InsP(3) BM. Immunocytochemistry indicated a co-localisation of peripheral, junctional ryanodine receptors with InsP(3)Rs. Thus, the pronounced arrhythmogenic potency of ET-1 is due to the spatially specific recruitment of Ca(2+) sparks by subsarcolemmal InsP(3)Rs. Summation of such sparks efficiently generates delayed after depolarisations that trigger premature action potentials. We conclude that the particular spatial profile of cellular Ca(2+) signals is a major, previously unrecognised, determinant for arrhythmogenic potency and that the InsP(3) signalling cassette might therefore be a promising new target for understanding and managing atrial arrhythmia.

Action Potentials↗