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Biomedical subjects

Jutta Schaper

Publications and source records attributed to Jutta Schaper.

34 records · Page 2Linked to original sources
PubMed2004

Morphological changes of the aortic valve leaflets in non-compliant aortic roots: in-vivo experiments.

BACKGROUND AND AIM OF THE STUDY: Age-related loss of elasticity of the naturally compliant aortic root disrupts the coordinated function of the valve leaflets. Morphological changes that developed over time in the aortic valve leaflets of non-compliant aortic roots were studied. METHODS: Stiffening of the aortic roots was achieved in vivo by applying Super Glue around the sinus of Valsalva in 27 New Zealand White rabbits. In nine animals, glue was applied only partially, and eight untreated rabbits served as controls. Histological evaluation of the aortic valves was performed at 8-11 months after surgery, and included immunohistochemistry and confocal microscopy with quantitative tissue assessment. Levels of collagen I, as a main component of fibrosis, and matrix metalloproteinases (MMP)-1 and MMP-9 and angiotensin-converting enzyme (ACE), as regulators of fibrosis, were analyzed. The morphological structure of the aortic valve leaflets was studied, and the length, thickness and area of leaflets were measured. RESULTS: Leaflects in all groups were found to be composed of a continuous layer of collagen fibers at the mural side, and loose connective tissue containing fibroblasts and few capillaries on the aortic luminal aspect. In stiffened aortic roots, the length and area of the leaflets were increased. The area occupied by collagen was elevated in non-compliant aortic root leaflets, but collagen fluorescence intensity was decreased, indicating less densely packed collagen fibers. Degradation and synthesis of collagen as reflected by MMP-1, MMP-9 and ACE levels was up-regulated. CONCLUSION: Loss of compliance in aortic roots leads to elongation of the leaflets which, combined with a decrease in collagen density, may render leaflets more susceptible to mechanical stress. In time, this may promote the development of degenerative changes in the aortic valve.

Animals↗
PubMed2003

Myocytes die by multiple mechanisms in failing human hearts.

We tested the hypothesis that myocyte loss in failing human hearts occurs by different mechanisms: apoptosis, oncosis, and autophagic cell death. Explanted hearts from 19 patients with idiopathic dilated cardiomyopathy (EF< or =20%) and 7 control hearts were analyzed. Myocyte apoptosis revealed by caspase-3 activation and TUNEL staining occurred at a rate of 0.002+/-0.0005% (P<0.05 versus control) and oncosis assessed by complement 9 labeling at 0.06+/-0.001% (P<0.05). Cellular degeneration including appearance of ubiquitin containing autophagic vacuoles and nuclear disintegration was present at the ultrastructural level. Nuclear and cytosolic ubiquitin/protein accumulations occurred at 0.08+/-0.004% (P<0.05). The ubiquitin-activating enzyme E1 and the ligase E3 were not different from control. In contrast, ubiquitin mRNA levels were 1.8-fold (P<0.02) elevated, and the conjugating enzyme E2 was 2.3-fold upregulated (P<0.005). The most important finding, however, is the 2.3-fold downregulation of the deubiquitination enzyme isopeptidase-T and the 1.5-fold reduction of the ubiquitin-fusion degradation system-1, which in conjunction with unchanged proteasomal subunit levels and proteasomal activity results in massive storage of ubiquitin/protein complexes and in autophagic cell death. A 2-fold decrease of cathepsin D might be an additional factor responsible for the accumulation of ubiquitin/protein conjugates. It is concluded that in human failing hearts apoptosis, oncosis, and autophagy act in parallel to varying degrees. A disturbed balance between a high rate of ubiquitination and inadequate degradation of ubiquitin/protein conjugates may contribute to autophagic cell death. Together, these different types of cell death play a significant role for myocyte disappearance and the development of contractile dysfunction in failing hearts.

Apoptosis↗
PubMed2003

Progression from compensated hypertrophy to failure in the pressure-overloaded human heart: structural deterioration and compensatory mechanisms.

BACKGROUND: The progression of compensated hypertrophy to heart failure (HF) is still debated. We investigated patients with isolated valvular aortic stenosis and differing degrees of left ventricular (LV) systolic dysfunction to test the hypothesis that structural remodeling, as well as cell death, contributes to the transition to HF. METHODS AND RESULTS: Structural alterations were studied in LV myectomies from 3 groups of patients (group 1: ejection fraction [EF] >50%, n=12; group 2: EF 30% to 50%, n=12; group 3: EF <30%, n=10) undergoing aortic valve replacement. Control patients were patients with mitral valve stenosis but normal LV (n=6). Myocyte hypertrophy was accompanied by increased nuclear DNA and Sc-35 (splicing factor) content. ACE and TGF-beta1 were upregulated correlating with fibrosis, which increased 2.3-, 2.2-, and 3.2-fold over control in the 3 groups. Myocyte degeneration increased 10, 22, and 32 times over control. A significant correlation exists between EF and myocyte degeneration or fibrosis. Ubiquitin-related autophagic cell death was 0.5 per thousand in control and group 1, 1.05 in group 2, and 6.05 per thousand in group 3. Death by oncosis was 0 per thousand in control, 3 per thousand in group 1, and increased to 5 per thousand (groups 2 and 3). Apoptosis was not detectable in control and group 3, but it was present at 0.02 per thousand in group 1 and 0.01 per thousand in group 2. Cardiomyocyte mitosis was never observed. CONCLUSIONS: These structure-function correlations confirm the hypothesis that transition to HF occurs by fibrosis and myocyte degeneration partially compensated by hypertrophy involving DNA synthesis and transcription. Cell loss, mainly by autophagy and oncosis, contributes significantly to the progression of LV systolic dysfunction.

Aged↗
PubMed2003

Regulation of EMAP II by hypoxia.

Endothelial-monocyte-activating polypeptide II (EMAP II) is a proinflammatory cytokine and a chemoattractant for monocytes and granulocytes. We have previously shown that EMAP II mRNA is strongly expressed at sites of apoptosis in the mouse embryo and that the mature protein is cleaved from its cellular precursor (proEMAP II/p43) by caspase activation to become released from cells. Here we demonstrate in vivo that EMAP II mRNA expression is strongly increased in tumor necrosis factor alpha (TNF)-treated murine meth A fibrosarcomas and in B16 melanomas, especially in close proximity to areas of tissue necrosis. Furthermore, by means of confocal microscopy, high level expression of proEMAP II/p43 protein correlated predominantly with hypoxic but also with apoptotic cells. In vitro, EMAP II mRNA levels were not increased by hypoxia. However, high amounts of mature EMAP II protein were detected in the supernatants of hypoxic tumor cells. Unlike in apoptotic cells, neither a broad-range caspase inhibitor nor an inhibitor specific for the internal cleavage site was able to inhibit processing of proEMAP II/p43 to the mature EMAP II protein. In conclusion, these data suggest that hypoxia and apoptosis provide two alternative mechanisms of EMAP II generation by tumor cells.

Animals↗
PubMed2003

Cardiac overexpression of monocyte chemoattractant protein-1 in transgenic mice mimics ischemic preconditioning through SAPK/JNK1/2 activation.

OBJECTIVE AND METHODS: Although a beneficial association between innate immunity and ischemic preconditioning has recently been proposed, the mechanisms responsible for this link are poorly understood. To test the hypothesis that pro-inflammatory cytokines have a beneficial role in the activation of the cell survival pathway mediated by ischemic preconditioning, we have studied transgenic mice with cardiac myocyte specific overexpression of murine monocyte chemoattractant protein-1 (MCP-1). The resistance to ischemia was studied by performing 45-min (with or without injection of the SAPK/JNKs inhibitor D-JNKI1) and 3-day left coronary artery occlusions as well as 45-min left coronary artery occlusion followed by 3 days of reperfusion. In addition, quantitative Western blot analyses for TNF-alpha, and SAPK/JNK1/2, ERK1/2 and p38 activity were performed. RESULTS: Infarct size, expressed in percent of either the risk area or the left ventricle, was reduced in transgenic mice when compared with control after both, 45-min (14.7+/-2.6% vs. 52.0+/-2.4%; P<0.05) and 45-min occlusion followed by 3 days of reperfusion (23.2+/-1.8% vs. 30.0+/-1.8%; P<0.05) but it was not significantly different for 3-day occlusion. Western blot analyses showed significantly increased levels of TNF-alpha (1.8-fold) and phosphorylated-SAPK/JNK1/2 (1.5-fold) in transgenic hearts. Phosphorylated-ERK1/2, and phosphorylated-p38 levels were unchanged. Immunohistochemistry revealed that in transgenic mice monocytes/macrophages, lymphocytes, and fibroblasts are the source of TNF-alpha, whereas myocytes have increased phosphorylated-SAPK/JNK1/2 levels. In addition, injection of the SAPK/JNKs inhibitor D-JNKI1 partially abrogated the cardioprotective effect observed in untreated transgenic mice. CONCLUSION: Overexpression of MCP-1 by cardiomyocytes causes chronic infiltration and activation of leukocytes, resulting in elevated TNF-alpha secretion and SAPK/JNK1/2 activation. The activation of this pathway is in part responsible for the preconditioning effect of MCP-1 overexpression. These results show a possible beneficial link between innate immunity and ischemic preconditioning through MAP-kinase activation.

Animals↗
PubMed2003

Increased glycolysis as protective adaptation of energy depleted, degenerating human hibernating myocardium.

In the current study on human hibernating myocardium (HHM), we tested the hypothesis that increased glycolysis might exert a positive effect during a supply-demand balance situation by augmentation of myocardial energy formation. In 14 patients HHM was preoperatively detected by clinical methods and validated by the recovery of contractile function three months following revascularization. During open-heart surgery, transmural biopsies were removed from the hibernating areas and analyzed using biochemical and morphologic methods. Metabolite contents were normalized for the degree of fibrosis (control: 9.8 +/- 0.5%, HHM 28.1 +/- 3.0%; p < 0.05), providing values for cardiomyocytes only. In energy depleted HHM, severe intracellular degeneration, glycogen accumulation and myocyte loss were found. Elevated lactate levels (2.22 +/- 0.26 vs. 25.38 +/- 3.53 micromol/wet wt, p < 0.001) were indicative of an increased anaerobic glycolytic flux. In conclusion the presence of abundant intracellular glycogen and an increased anaerobic glycolysis in HHM is indicative of a protective adaptation of this myocardium, which might balance energy deficit and may limit structural damage.

Adaptation, Physiological↗
PubMed2003

Gap junction remodeling and altered connexin43 expression in the failing human heart.

Gap junctions (GJ) are important determinants of cardiac conduction and the evidence has recently emerged that altered distribution of these junctions and changes in the expression of their constituent connexins (Cx) may lead to abnormal coupling between cardiomyocytes and likely contribute to arrhythmogenesis. However, it is largely unknown whether changes in the expression and distribution of the major cardiac GJ protein, Cx43, is a general feature of diverse chronic myocardial diseases or is confined to some particular pathophysiological settings. In the present study, we therefore set out to investigate qualitatively and quantitatively the distribution and expression of Cx43 in normal human myocardium and in patients with dilated (DCM), ischemic (ICM), and inflammatory cardiomyopathies (MYO). Left ventricular tissue samples were obtained at the time of cardiac transplantation and investigated with immunoconfocal and electron microscopy. As compared with the control group, Cx43 labeling in myocytes bordering regions of healed myocardial infarction (ICM), small areas of replacement fibrosis (DCM) and myocardial inflammation (MYO) was found to be highly disrupted instead of being confined to the intercalated discs. In all groups, myocardium distant from these regions showed an apparently normal Cx43 distribution at the intercalated discs. Quantitative immunoconfocal analysis of Cx43 in the latter myocytes revealed that the Cx43 area per myocyte area or per myocyte volume is significantly decreased by respectively 30 and 55% in DCM, 23 and 48% in ICM, and by 21 and 40% in MYO as compared with normal human myocardium. In conclusion, focal disorganization of GJ distribution and down-regulation of Cx43 are typical features of myocardial remodeling that may play an important role in the development of an arrhythmogenic substrate in human cardiomyopathies.

Adult↗
PubMed2002

The cardiac mechanical stretch sensor machinery involves a Z disc complex that is defective in a subset of human dilated cardiomyopathy.

Muscle cells respond to mechanical stretch stimuli by triggering downstream signals for myocyte growth and survival. The molecular components of the muscle stretch sensor are unknown, and their role in muscle disease is unclear. Here, we present biophysical/biochemical studies in muscle LIM protein (MLP) deficient cardiac muscle that support a selective role for this Z disc protein in mechanical stretch sensing. MLP interacts with and colocalizes with telethonin (T-cap), a titin interacting protein. Further, a human MLP mutation (W4R) associated with dilated cardiomyopathy (DCM) results in a marked defect in T-cap interaction/localization. We propose that a Z disc MLP/T-cap complex is a key component of the in vivo cardiomyocyte stretch sensor machinery, and that defects in the complex can lead to human DCM and associated heart failure.

Adult↗
PubMed2002

Remodeling of the adventitia during coronary arteriogenesis.

We studied the role of the adventitia in adaptive arteriogenesis during the phase of active growth of coronary collateral vessels (CV) induced by chronic occlusion of the left circumflex coronary artery in canine hearts. We used electron microscopy and immunoconfocal (IF) labeling for bFGF, matrix metalloproteinase (MMP)-2, MMP-9, tissue-type plasminogen activator (tPA), its inhibitor (PAI-1), fibronectin (FN), and Ki-67. Proliferation of smooth muscle cells and adventitial fibroblasts was evident. Quantitative IF showed that adventitial MMP-2, MMP-9, and FN were 9.2-, 7.5-, and 8.6-fold, bFGF was 5.1-fold, and PAI-1 was 3.4-fold higher in CV than in normal vessels (NV). The number of fibroblasts was 5-fold elevated in CV, but the elastic fiber content was 25-fold greater in NV than in CV. Perivascular myocyte damage and induction of endothelial nitric oxide synthase in peri-CV capillaries indicate expansion of CV. It was concluded that adventitial activation is associated with the development of CV through cell proliferation, production of growth factors, and induction of extracellular proteolysis thereby contributing to remodeling during adaptive arteriogenesis.

Animals↗
PubMed2002

Metabolic control analysis of anaerobic glycolysis in human hibernating myocardium replaces traditional concepts of flux control.

Myocardial hibernation represents an adaptation to sustained ischemia to maintain tissue vitality during severe supply-demand imbalance which is characterized by an increased glucose uptake. To elucidate this adaptive protective mechanism, the regulation of anaerobic glycolysis was investigated using human biopsies. In hibernating myocardium showing an increase in anaerobic glycolytic flux metabolizing exogenous glucose, the adjustment of flux through this pathway was analyzed by flux:metabolite co-responses. By this means, a previously unknown pattern of regulation using multisite modulation was found which largely differs from traditional concepts of metabolic control of the Embden-Meyerhof pathway in normal and diseased myocardium.

Anaerobiosis↗
PubMed2002

Structural correlate of atrial fibrillation in human patients.

OBJECTIVE: We tested the hypothesis that structural remodeling of cellular connections, alterations in the expression of connexins (Cx), and an increase in fibrosis represent anatomic substrates of atrial fibrillation (AF). METHODS: In 31 patients with AF undergoing a Maze procedure and 22 patients in sinus rhythm (SR), biopsies were taken intraoperatively from the right atrial (RA) free wall and appendages and investigated with immunoconfocal and electron microscopy. RESULTS: All patients with AF exhibited a concomitant lateralization of gap junctional proteins Cx43 and Cx40, and N-cadherin (the major mechanical junction protein), instead of being confined to the intercalated discs, as observed in SR. These results were confirmed by quantitative immunoconfocal analysis and electron microscopy. Among diverse junctional proteins, in AF, Cx40 was markedly heterogeneous in distribution. As compared with the SR group, Cx43 was significantly decreased in AF by 57% in RA appendages and by 56% in RA free wall. Cx40 was reduced by 54% in appendages, but had a tendency to be increased in the RA free wall. Collagen I was significantly higher in AF than in SR by 48% in RA appendages and by 69% in the RA free wall tissues. CONCLUSIONS: The structural correlate of AF comprises extensive concomitant remodeling of mechanical and electrical junctions, reduction of Cx43, heterogeneous distribution of Cx40 in terms of different amounts of Cx40 in different RA tissues or in spatially adjacent regions of atrial myocardium. These changes, together with augmentation of fibrosis, may underlie localized conduction abnormalities and contribute to initiation and self-perpetuation of re-entry pathways and AF.

Aged↗
PubMed2002

Changes in the preserved heart that limit the length of preservation.

BACKGROUND: The variability in donor heart viability following preservation is well known and very dependent on the animal model used and the methods of preservation. Using hypothermia (2 to 4 degrees C) with the University of Wisconsin solution and microperfusion (3 microl/g/min) myocardial functional recovery after reperfusion is 50% to 60% after 18 hours of preservation. Many investigators have found the 18-hour preservation barrier for functional recovery of the heart with different experimental protocols. In previous studies, we have found in normothermic global ischemia that with necrosis there was a significant amount of apoptosis. It was therefore the purpose of this study to investigate the importance of apoptosis in heart preservation and determine if this cellular disruption plays a part in limiting heart viability during recovery from preservation. METHODS: Using a heterotopic heart transplant model, myocardial function (end-systolic elastance), high energy phosphate changes, metabolic substrate utilization, electron microscopy to determine degree of injury, and histologic changes that included apoptosis and lamin B(1) analyses were conducted on canine hearts preserved for 18 hours and reperfused for 6 hours. The changes were compared with a control group with no preservation. RESULTS: The 18-hour preserved heart regained approximately 50% to 60% of its original function, with significant decreases in adenosine triphosphate, no irreversible cellular changes (necrosis), and a 6% to 8% increase in apoptotic myocytes with a concomitant 8% decrease in lamin B(1). CONCLUSIONS: Preserved hearts can be maintained for approximately 12 hours with functional recovery near normal. However, approaching 18 hours, there is an attenuated functional response which may be related to the to development of apoptosis.

Animals↗
PubMed2002

Weakness of a giant: mutations of the sarcomeric protein titin.

In 2002, three reports described for the first time mutations in the sarcomeric protein titin associated with dilated cardiomyopathy in humans. Despite different locations (Z-line region, Z-I transitional zone, N2B region, half A band region) all mutations resulted in heart failure. In addition, an N2B mutation was found in zebrafish embryos with ventricular dilatation and cardiac insufficiency. It is concluded that titin mutations have significant functional consequences and need to be studied intensively in the future.

Cardiomyopathy, Dilated↗
PubMed2002

Apoptosis in myocardial infarction.

Apoptosis, one of the major forms of cell death, has been implicated in different cardiovascular diseases. In this paper we review many of the different studies that have been performed to address the occurrence of apoptotic cell death associated with myocardial infarction. A definitive differentiation between apoptosis and other forms of cell death is still needed, mainly because of differences and limitations of the methods used for detection. In myocardial infarction apoptosis has been reported at acute stages of evolution in the ischemic area as well as in remote zones. In the ischemic area it might be a determinant of the final size of the infarct and it seems to depend on the presence of post-ischemic reperfusion. However, the incidence of apoptosis reported until now varies widely. In the myocardium remote from the ischemic area it might be associated with the progression towards heart failure. At present, the role and significance of apoptosis in myocardial infarction is rather inconclusive. Further studies are needed to solve methodological uncertainties and clarify the mechanisms involved in the process of cell death, which is particularly important as a basis for therapeutic interventions.

Animals↗
PubMed2002

The carboxyl-terminal region of ahnak provides a link between cardiac L-type Ca2+ channels and the actin-based cytoskeleton.

Ahnak is a ubiquitously expressed giant protein of 5643 amino acids implicated in cell differentiation and signal transduction. In a recent study, we demonstrated the association of ahnak with the regulatory beta2 subunit of the cardiac L-type Ca2+ channel. Here we identify the most carboxyl-terminal ahnak region (aa 5262-5643) to interact with recombinant beta2a as well as with beta2 and beta1a isoforms of native muscle Ca2+ channels using a panel of GST fusion proteins. Equilibrium sedimentation analysis revealed Kd values of 55 +/- 11 nM and 328 +/- 24 nM for carboxyl-terminal (aa 195-606) and amino-terminal (aa 1-200) truncates of the beta2a subunit, respectively. The same carboxyl-terminal ahnak region (aa 5262-5643) bound to G-actin and cosedimented with F-actin. Confocal microscopy of human left ventricular tissue localized the carboxyl-terminal ahnak portion to the sarcolemma including the T-tubular system and the intercalated disks of cardiomyocytes. These results suggest that ahnak provides a structural basis for the subsarcolemmal cytoarchitecture and confers the regulatory role of the actin-based cytoskeleton to the L-type Ca2+ channel.

Actin Cytoskeleton↗