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Biomedical subjects

G Plenz

Publications and source records attributed to G Plenz.

At least 19 recordsLinked to original sources
PubMed2004

[Mechanisms of transplant vasculopathy].

Cardiac allograft vasculopathy is a diffuse, obliterative form of arteriosclerosis that is characterized by the production of a neointima rich in vascular smooth muscle cells that progressively obstructs the lumen. Pathophysiologically, after heart transplantation, alloantigens (e. g. on donor endothelial cells) are presented by antigen presenting cells to the T-cells of the body's immune system. With the appropriate costimulatory signal, this signal pattern generates a differentiated T-cell, B-cell, and inflammatory cell response whereas without the second signal, the immune cells undergo apoptosis. In case of immune cell proliferation and differentiation, a coordinated pattern of cytokine release is initiated. Cells of innate immunity, monocyte-derived macrophages, are involved in this process. The inflammatory response culminates in rolling, sticking, and diapedesis through the coronary vascular endothelium and migration and phenotype switch of medial smooth muscle cells mediated by generation of growth-promoting cytokines.

Animals↗
PubMed2001

Cellular localization, membrane distribution, and possible function of guanylyl cyclases A and 1 in collecting ducts of rat.

BACKGROUND: Natriuretic peptides regulate Na+ and H(2)O transport in the cortical collecting duct (CCD). We have shown that natriuretic peptides have no effect on ion conductances or water transport of principal cells (PC) even though a cGMP-regulated K+ channel is located in the basolateral membrane of these cells. METHODS: RT-PCR was used to screen for different guanylyl cyclases (GC) in CCD and to look for the expression of GC-1 and GC-A mRNA in CCD of male and female Wistar and Sprague-Dawley rats. Polyclonal antibodies were raised against the detected GC. BCECF was used to investigate the effects of ANP on intracellular pH in intercalated cells (IC). RESULTS: GC-A and GC-1 were detected. GC-A was immunolocalized in the luminal membrane of IC while GC-1 was mainly found in the luminal membrane of PC. GC-1 is expressed in Sprague-Dawley and Wistar rats except for male Sprague-Dawley rats, while GC-A is expressed in all strains. ANP (160 nM, n=11), urodilatin (140 nM, n=6), which had no effect in PC, significantly decreased pH(i) by 0.02+/-0.01 and 0.03 +/- 0.01 Units in IC, respectively. ANP as well as urodilatin and 8-Br-cGMP decreased the pH(i) recovery after acidification by 30 +/- 6% (n=12), 37 +/- 7% (n=8), and 19 +/- 3% (n=8), respectively. CONCLUSION: GC-A is located in the luminal membrane of IC of rat CCD and ANP acts through this receptor when regulating pH(i) via an inhibition of the Na+/H+-exchanger. PC do not possess GC-A. GC-1 seems to be the only GC in these cells of most rat strains tested and therefore, it could be responsible for the regulation of K+ channels in the basolateral membrane via cGMP-dependent protein kinase.

Animals↗
PubMed2001

Alteration of fracture stability influences chondrogenesis, osteogenesis and immigration of macrophages.

Mechanical conditions at the fracture line determine the mode of fracture healing (osteonal versus non-osteonal bone union). The aim of this study was to investigate the influence of differing degrees of fracture stability on the time course of chondrogenesis, enchondral ossification and immigration of macrophages into the fracture callus. Using a fracture model of the rat's tibia, histological (Azan staining), immunohistological (antibodies directed against the macrophage-specific surface antigen ED2), and molecular biological techniques (expression of the mRNA of the cartilage-specific collagen IX, osteocalcin - a marker for mature osteoblasts - and the macrophage-specific macrosialin) were employed. In terms of histology and molecular biology (collagen IX mRNA expression) chondrogenesis in the fracture gap continued for longer in less stable fractures. In more stable fractures bone formation - identified by osteocalcin mRNA expression - increased from day 12 onwards. The expression of the macrophage-specific surface antigen ED2 and the mRNA of macrosialin was more pronounced but of shorter duration in the more stable fractures. This study shows that differing degrees of fracture stability not only influence the interplay between osteogenesis and chondrogenesis but also alter the kinetics of macrophage immigration into the fracture callus. These findings could aid in better understanding the cytobiologic mechanisms of callus formation and may suggest that macrophages are an important factor not only in soft tissue healing but also in bone healing.

Animals↗
PubMed2001

Activation of the cardiac interleukin-6 system in advanced heart failure.

OBJECTIVES: The study objective was to assess the cardiac expression of interleukin-6 (IL6) and its receptor (IL6R) in advanced heart failure. BACKGROUND: While IL6 plasma levels are elevated and associated with an impaired prognosis in advanced heart failure, little is known about the intracardiac expression of the IL6 system. METHODS: Heart tissue was obtained from 20 patients (n=10, idiopathic dilated cardiomyopathy, age 44+/-15 years; n=10, ischemic cardiomyopathy, age 55+/-8 years) at the time of transplantation. Left and right ventricular tissue was subjected to in situ hybridization, Northern blot analysis, and RT-PCR. Signals were quantified by densitometric scanning and corrected for G3PDH-mRNA levels. Right ventricular biopsy specimens (n=11) of patients with arrhythmias and normal cardiac function served as controls. In addition, data were correlated with cardiac catheterization and echocardiography data obtained at transplant evaluation. RESULTS: Ventricular IL6 and IL6R transcripts were detected in all explant specimens examined. Expression of both mRNA species was higher than in controls (P=0.001). Left ventricular IL6 mRNA levels correlated positively with heart rate (r=0.77; P=0.009), pulmonary capillary wedge pressure (r=0.53; P=0.03), right atrial pressure (r=0.77; P=0.003), and inversely with left ventricular ejection fraction (r=-0.61; P=0.03). Right ventricular IL6 mRNA levels correlated inversely with cardiac index (r=-0.48; P=0.05). IL6R expression did not correlate with hemodynamic data. CONCLUSIONS: In advanced heart failure, cardiac IL6/IL6R mRNA expression is increased and may play a role in the pathophysiology of advanced heart failure.

Adult↗
PubMed2000

Transplant vasculopathy: a model for coronary artery disease?

Although transplant vasculopathy and native atherosclerosis are clinically and pathologically different entities, the pathogenesis of both diseases exhibits some common mechanisms. Both may be regarded as responses to injury within a broadened concept of the immune system. Alloantigens (e.g. on donor endothelial cells) or autoantigens (e.g. oxydized LDL cholesterol) are presented by antigen presenting cells to the T cells of the body's immune system. With the appropriate costimulatory signal, this signal pattern generates a differentiated T cell, B cell, and inflammatory cell response whereas without the second signal, the immune cells undergo apoptosis. In case of immune cell proliferation and differentiation, a coordinated pattern of cytokine release is initiated. Monocyte-derived macrophages are also involved in this process which culminates in rolling, sticking, and diapedesis through the coronary vascular endothelium and phenotype switch of medial smooth muscle cells mediated by generation of growth-promoting cytokines. Thus, viewed within a broadened paradigm of the immune system's role both disease entities may represent different vignettes of an integrated pathophysiological response to an endothelial injury.

Animals↗
PubMed2000

Reversal of metallothionein expression is different throughout the human myocardium after prolonged left-ventricular mechanical support.

OBJECTIVES: We examined the distribution of metallothionein (MT), a stress-inducible protein, and the cardiomyocyte diameter in human hearts after left-ventricular assist device (LVAD) support. BACKGROUND: Remodeling in end-stage heart failure is characterized by myocyte hypertrophy and alterations of several inducible proteins. LVADs used as a bridge to cardiac transplantation unload the left ventricle and may lead to a reversal of the remodeling, but little is known about the pathophysiology of this process. METHODS: The immunoreactivity for MT and the cardiomyocyte diameter was analyzed in left-ventricular tissue specimens of 17 patients with end-stage heart failure before and after LVAD support. RESULTS: MT positive cells were mainly located sub-endocardially in vacuolized cardiomyocytes and in small vessels throughout the myocardium. During LVAD support, MT-positive myocytes decreased in the sub-endocardial (p < 0.008) and sub-epicardial region (p < 0.003), MT-positive vessels decreased similarly (p < 0.003). Cardiomyocyte diameter decreased significantly only in the sub-endocardium (p < 0.03). Hearts of patients supported longer than 88 days (= median) showed substantially lower MT reactivity at the time of LVAD explantation as compared to patients supported less than 88 days. CONCLUSION: Our results suggest that unloading of the left ventricle during prolonged LVAD support leads to regression of cellular hypertrophy and a decrease of MT expression. The preferential reduction of MT-positive vacuolized cardiomyocytes in the sub-endocardium is comparable with the concept of greatest reduction of wall stress in this area of the myocardium and may be due to the improvement of myocardial blood flow and the energy balance.

Adult↗
PubMed1999

Colony stimulating factors modulate the transcription of type VIII collagen in vascular smooth muscle cells.

Colony stimulating factors belong to a family of cytokines that regulate proliferation in macrophages and other vascular cell types. They have been implicated in the inflammatory-fibroproliferative response of atherosclerosis. The present study was undertaken to assess the effect of granulocyte-macrophage and macrophage colony stimulating factors on the transcription of type VIII collagen by vascular smooth muscle cells and their potential relevance for the expression of collagen in atherosclerotic lesions. The influence of colony stimulating factors was studied in relation to transforming growth factor beta1, the factor exhibiting the most potent effect on collagen metabolism. Northern blot experiments showed that treatment with both colony stimulating factors and transforming growth factor beta1 transiently stimulated the transcription of type VIII collagen mRNA. Maximal levels were reached after 2 h and 100 pg/ml granulocyte macrophage colony stimulating factor (4-fold), 1 U/ml macrophage colony stimulating factor (4.6-fold) and 1 ng/ml transforming growth factor beta1 (1.6-fold). While overnight treatment with colony stimulating factors stimulated the expression of transforming growth factor beta1 mRNA, short incubations did not influence or downregulate the transcription. In turn, treatment with transforming growth factor beta1 reduced the expression of granulocyte-macrophage and macrophage colony stimulating factor mRNA. The in vitro mRNA expression patterns were directly reflected in the distribution patterns found in intimal thickenings and advanced atherosclerotic lesions. This study demonstrates that colony stimulating factors and transforming growth factor beta1 modulate the transcription of type VIII collagen in vitro. Our data indicate a direct mechanism and exclude a pathway, which is mediated via the stimulation of transforming growth factor beta1 transcription. Our studies further support the hypothesis that colony stimulating factors in concert with transforming growth factor beta1 affect the collagenous composition of the extracellular vascular matrix.

Arteriosclerosis↗
PubMed1999

Paracrine or virus-mediated induction of decorin expression by endothelial cells contributes to tube formation and prevention of apoptosis in collagen lattices.

Resting endothelial cells express the small proteoglycan biglycan, whereas sprouting endothelial cells also synthesize decorin, a related proteoglycan. Here we show that decorin is expressed in endothelial cells in human granulomatous tissue. For in vitro investigations, the human endothelium-derived cell line, EA.hy 926, was cultured for 6 or more days in the presence of 1% fetal calf serum on top of or within floating collagen lattices which were also populated by a small number of rat fibroblasts. Endothelial cells aligned in cord-like structures and developed cavities that were surrounded by human decorin. About 14% and 20% of endothelial cells became apoptotic after 6 and 12 days of co-culture, respectively. In the absence of fibroblasts, however, the extent of apoptosis was about 60% after 12 days, and cord-like structures were not formed nor could decorin production be induced. This was also the case when lattices populated by EA.hy 926 cells were maintained under one of the following conditions: 1) 10% fetal calf serum; 2) fibroblast-conditioned media; 3) exogenous decorin; or 4) treatment with individual growth factors known to be involved in angiogenesis. The mechanism(s) by which fibroblasts induce an angiogenic phenotype in EA.hy 926 cells is (are) not known, but a causal relationship between decorin expression and endothelial cell phenotype was suggested by transducing human decorin cDNA into EA.hy 926 cells using a replication-deficient adenovirus. When the transduced cells were cultured in collagen lattices, there was no requirement of fibroblasts for the formation of capillary-like structures and apoptosis was reduced. Thus, decorin expression seems to be of special importance for the survival of EA.hy 926 cells as well as for cord and tube formation in this angiogenesis model.

Adenoviridae↗
PubMed1999

Inverse relationship between connexin43 and desmin expression in cultured porcine aortic smooth muscle cells.

Our previous work has shown that in vascular tissues the elastic medial regions express high levels of the gap junctional protein, connexin43, but low levels of desmin, while the muscular medial regions express low levels of connexin43 but high levels of desmin. It is uncertain, however, whether this regional difference at the tissue level extends down to the level of the individual cell, or reflects an averaged relationship of groups of cells of different connexin43 and desmin expression. The present study has addressed this question using cultured porcine aortic smooth muscle cells. Immunoconfocal microscopic analysis of single-labeled cells showed that while smooth muscle alpha-actin, calponin and vimentin were positively labeled in the majority of medial smooth muscle cells both in intact porcine aorta and corresponding cultured cells, desmin and connexin43 labeling was highly heterogeneous. In the cultured cells, 0.3-0.5% of cells were found to be desmin-positive, and quantitative analysis after double labeling for desmin and connexin43 revealed that the desmin-positive cells were smaller, and contained significantly lower numbers and smaller sizes of connexin43 gap-junctional spots than did desmin-negative cells. Our findings demonstrate that an inverse expression pattern of connexin43 and desmin holds true at the level of the individual cell. This suggests a close relationship between intrinsic phenotypic control and the regulation of connexin43 expression in the arterial smooth muscle cell.

Actins↗
PubMed1999

Metallothionein: localization in human transplant endomyocardium, relation to cytokines and allograft function.

BACKGROUND: The aim of this study was to investigate the role of metallothionein in cardiac transplants in relation to cytokines and allograft function. Recent studies have revealed an association of allograft dysfunction with elevated proinflammatory cytokines independent of cellular rejection. In animal experiments, cytokines induced overexpression of metallothionein, a low-molecular-weight protein implicated in cellular stress response. METHODS: In 105 consecutive biopsies from 15 patients during the first 3 months after heart transplantation, metallothionein expression was investigated immunohistochemically. Its relation to serum interleukin-6, tumor necrosis factor-alpha, interleukin-2 (IL-2), soluble interleukin-2 receptor rejection, and echocardiographic parameters was determined. Forty-three biopsies of 12 patients with idiopathic ventricular tachycardia served as controls. RESULTS: Metallothionein expression was demonstrated in small vessels, cardiomyocytes, fibrocytes, and interstitial round cells. A positive relation between interleukin-6 levels and the number of metallothionein-positive small vessels (p < 0.028) was observed. Patients with lower serum IL-2 levels showed significantly higher numbers of metallothionein-positive small vessels (p < 0.043). Grafts with prolonged ischemic time (>150 minutes) showed a significantly higher myocardial metallothionein score (p < 0.021). Metallothionein expression was associated with lower fractional shortening, larger left ventricular end-systolic diameter, and lower mean arterial pressure but not with acute cellular rejection. CONCLUSIONS: Metallothionein expression is associated with elevated interleukin-6 and decreased interleukin-2 serum levels and left ventricular allograft dysfunction in the absence of rejection.

Acute Disease↗
PubMed1999

Human macrophages synthesize type VIII collagen in vitro and in the atherosclerotic plaque.

Type VIII collagen is a short-chain collagen that is present in increased amounts in atherosclerotic lesions. Although the physiological function of this matrix protein is unclear, recent data suggest an important role in tissue remodeling. Type VIII collagen in the atherosclerotic lesion is mainly derived from smooth muscle cells. We now show that macrophages in the atherosclerotic vessel wall and monocytes in adjacent mural thrombi also express type VIII collagen. We demonstrated this using a novel combined fluorescence technique that simultaneously stains, within the same tissue section, specific RNAs by in situ hybridization and proteins by indirect immunofluorescence. In culture, human monocyte/macrophages expressed type VIII collagen at all time points from 1 h to 3 wk after isolation. Western blotting and immunoprecipitation also revealed secretion of type VIII collagen into the medium of 14-day-old macrophages. Because this is the first report of secretion of a collagen by macrophages, we tested the effect of lipopolysaccharide (LPS) and interferon gamma, substances that stimulate macrophages to secrete lytic enzymes, on macrophage expression of type VIII collagen. LPS and interferon gamma decreased expression of type VIII collagen. By contrast, secretion of matrix metalloproteinase 1 (MMP 1) was increased, indicating a switch from a collagen-producing to a degradative phenotype. Double in situ hybridization studies of expression of type VIII collagen and MMP 1 in human coronary arteries showed that in regions important for plaque stability, the ratio of MMP 1 RNA to macrophage type VIII collagen RNA varies widely, indicating that the transition from one phenotype to the other that we observed in vitro may also occur in vivo.

Cells, Cultured↗
PubMed1999

Cholesterol-induced changes of type VIII collagen expression and distribution in carotid arteries of rabbit.

Lipoproteins play a major role in cardiovascular disease and atherosclerosis. In the vascular wall, they strongly influence the organization of extracellular matrix. The present study set out to investigate the changes in the extracellular matrix of the vessel wall induced by atherogenic diet, focusing on type VIII collagen, a vascular collagen that has not previously been investigated in detail. The influence of cholesterol diet on the expression, distribution, and deposition of type VIII collagen was examined in carotid arteries of New Zealand White rabbits. Carotid arteries of rabbits receiving diet supplemented with 1% cholesterol for 6 weeks and those on the same regimen followed by normal chow for 1 day, 10 days, 5 weeks, and 12 weeks were studied and compared with controls not exposed to the cholesterol diet. Carotid arteries of normocholesterolemic rabbits contained type VIII collagen-expressing cells in all layers, with focal accumulations of expressing cells in the subendothelial areas, the outer medial zone, and the adventitia. In response to cholesterol diet, type VIII collagen synthesis was reduced in media and adventitia and the distribution patterns changed. Expressing cells were found predominantly in the endothelium, and type VIII collagen accumulated in the intimal space. Immunogold labeling for electron microscopy revealed that type VIII collagen in the intima is associated with microfibrils extending from the internal elastic lamina. Withdrawal of cholesterol resulted in reestablishment of the normal distribution pattern. Northern and Western blot analyses supported the immunoconfocal and in situ hybridization data, demonstrating decreased type VIII collagen expression in response to cholesterol diet and progressive recovery to normal levels with time after withdrawal of cholesterol. Our study demonstrates that type VIII collagen is modulated in the presence of cholesterol. The data indicate that type VIII collagen is specifically remodeled during early experimental atherosclerosis, implying a role for this extracellular matrix component in neointimal growth.

Animals↗
PubMed1999

Expression of type VIII collagen after cholesterol diet and injury in the rabbit model of atherosclerosis.

This study presents an analysis of the expression of type VIII collagen mRNA in response to cholesterol diet and balloon injury in the rabbit iliac artery. The design of the animal experiments was as follows: 28 male New Zealand White rabbits were divided into the 3 different treatment groups. Group 1 received regular chow; group 2 was fed with a 1% cholesterol diet for 6 weeks and normal chow for 5 weeks; and group 3 underwent balloon injury, then 6 weeks of a 1% cholesterol diet, which was followed by 5 weeks of normal chow. The expression pattern of type VIII collagen mRNA was compared with that of the fibrillar collagen types I and III, transforming growth factor-beta1, a factor known to exert the most potent stimulatory effect on collagen synthesis in vitro, and matrix metalloproteinase 1, a collagen-degrading enzyme. The cholesterol diet resulted in an upregulation of type VIII collagen, fibrillar collagens, transforming growth factor-beta1, and matrix metalloproteinase I in the adventitia. Although the number of type VIII collagen mRNA-expressing cells in the media increased, no significant difference in overall expression levels was detectable by northern blot analysis. The ratio of medial smooth muscle cells expressing type VIII collagen mRNA to those expressing type I and type III collagen mRNA (CVIII:CI:CIII) changed from 1:1.88:0.03 in the normal media to 1:0.78:0.29. When cholesterol feeding was preceded by balloon injury, type VIII collagen mRNA expression concomitant with the fibrillar collagens was further upregulated over and above that level reported after cholesterol diet alone. In general, low levels of transforming growth factor-beta1 mRNA correlated with high expression of matrix metalloproteinase I. Our study indicates that a cholesterol diet resulted in a balanced reorganization of the collagen composition but did not result in marked collagen accumulation. This may provide an extracellular environment that favors migration and proliferation processes during early atherogenesis. It also demonstrates that type VIII collagen is highly expressed and deposited at later stages, and this may be linked to processes such as tissue reorganization during vascular repair and plaque stabilization.

Animals↗
PubMed1999

Granulocyte-macrophage colony-stimulating factor (GM-CSF) modulates the expression of type VIII collagen mRNA in vascular smooth muscle cells and both are codistributed during atherogenesis.

The expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) and type VIII collagen was studied in human arteries. GM-CSF and type VIII collagen were codistributed in all layers of the walls of nondiseased arteries and during early atherogenesis with up to type V lesions. The number of cells expressing both mRNAs increased during the development of advanced atherosclerotic lesions. Whereas type VIII collagen expression increased further in complicated lesions, GM-CSF was downregulated. During early atherogenesis smooth muscle cells (SMC) and endothelial cells were the principal GM-CSF and type VIII collagen mRNA-expressing cell types. In advanced lesions monocytes/macrophages also expressed the mRNAs. In complicated lesions the number of GM-CSF mRNA-expressing SMC was markedly reduced. In in vitro experiments transforming growth factor-beta1, platelet-derived growth factor, and GM-CSF, but not basic fibroblast growth factor, stimulated the expression of type VIII collagen mRNA by SMC. GM-CSF transiently stimulated type VIII collagen transcription. Thus GM-CSF is a prominent component of the regulatory network influencing collagen metabolism during atherogenesis. By modulating the synthesis of type VIII collagen in SMC, GM-CSF may influence the course of plaque development and may govern processes such as cell movement, plaque stability, and thrombus organization.

Arteriosclerosis↗
PubMed1999

Differential expression of connexin43 and desmin defines two subpopulations of medial smooth muscle cells in the human internal mammary artery.

Upregulation of connexin43-gap junctions is associated with transition of contractile vascular smooth muscle cells (SMCs) to the synthetic state. To determine whether phenotypically distinct subpopulations of medial SMCs differentially express connexin43, we investigated the human distal internal mammary artery, a structurally heterogeneous vessel with features ranging from elastic to elastomuscular to muscular. Immunoconfocal microscopy combined with quantitative analysis and complemented by in situ hybridization showed that SMCs in the elastic medial regions expressed high levels of connexin43 but low levels of desmin, whereas those of muscular medial regions expressed low levels of connexin43 but high levels of desmin. Ultrastructurally, SMCs of both regions were of the contractile phenotype, but the former cells were irregular in shape with relatively prominent synthetic organelles whereas the latter were spindle shaped with fewer synthetic organelles. Vimentin, smooth muscle alpha-actin, calponin, h-caldesmon, and myosin heavy chains (SM1 and SM2) were equally highly expressed by most cells in both subpopulations. The connexin43/desmin expression pattern of SMCs in regions of intimal thickening resembled those of elastic medial regions. These findings refine the view suggested from previous studies that high levels of connexin43 expression are associated with SMCs of a less contractile/more synthetic phenotype. In the internal mammary artery, the 2 subpopulations of SMCs with markedly different connexin43 expression levels both represent a differentiated contractile phenotype, but the subpopulation showing high levels of connexin43-gap junctions is characterized by low levels of desmin and structural features that reflect a more synthetic tendency.

Aged↗