Acute Exercise-Induced Circulating Haematopoietic Stem and Progenitor Cells in Cardiac Patients - A Case Series.

BACKGROUND: Exercise-induced circulating haematopoietic stem and progenitor cell (HPC) number has been discussed in the context of regeneration in heart disease patients. OBJECTIVE: The aim of this pilot study was to compare the effect of different exercise protocols usually applied in cardiac rehabilitation on the number of acute, exercise-induced HPCs, related to potential mediators, e.g. biomarkers of sympathetic and oxidative stress, and inflammation. METHODS: This is a case series comprising seven patients suffering from coronary heart disease (CHD) undertaken at the Center for Ambulant Cardiac Rehabilitation. Patients (n=6) performed two exercise modes (constant-load, CLE; high-intensity interval, HIIE) in randomised order. Venous blood was drawn before and immediately after each test to assess CD34+/CD45+ HPC number by flow cytometry and biomarkers in blood plasma. The primary outcome was the change in HPC number, the secondary outcomes were changes in sympathetic/oxidative stress and markers of inflammation. RESULTS: Both exercise modes resulted in a non-significant increase in HPC number after exercise, even when the results of both tests were combined. Overall, free norepinephrine increased significantly and was positively related to exercise-induced HPC number (r=0.70, p<0.05). Markers of sympathetic activation (fNE), oxidative stress (myeloperoxidase) and inflammation (interleukin-6) significantly increased after CLE and HIIE with no difference between tests. CONCLUSIONS: Interestingly, acute CLE and HIIE did not stimulate significant HPC mobilisation in CHD, although both exercise modes elevated circulating concentrations of sympathetic activation. Haematopoietic stem and progenitor cell mobilisation could be blunted due to disease-related bone-marrow exhaustion.

Distribution of decidual natural killer cells and macrophages in the neighbourhood of the trophoblast invasion front: a quantitative evaluation.

STUDY QUESTION: Do decidual natural killer (dNK) cells and decidual macrophages (dMph) become enriched in the vicinity of the trophoblast invasion front? SUMMARY ANSWER: Morphometric image analysis and areal cell density calculations, which excluded observer bias, showed an enrichment of decidual leukocytes in the neighbourhood of the trophoblast invasion front. WHAT IS KNOWN ALREADY: In previous studies, the number of decidual leukocytes was visually counted in medium- or high power fields. These methods, however, cannot reveal the exact spatial relationship between leukocytes and invasive trophoblast cells, and are therefore prone to subjective errors. Thus, a more objective approach is required. STUDY DESIGN, SIZE, DURATION: Applying a new method of morphometric image analysis, leukocyte populations were studied in human tissue fragments derived from first trimester placentation sites (n = 7) as well as in co-cultures of first trimester decidual tissue with placental villi of the same pregnancy representing an appropriate in vitro model of trophoblast invasion (n = 15). PARTICIPANTS/MATERIALS, SETTINGS, METHODS: First trimester decidual tissue was obtained from women undergoing elective terminations of pregnancy at 7-10 weeks of gestational age. Tissue sections were double-stained immunohistochemically for markers of dNK cells or dMph on one hand, and for invasive extravillous trophoblast cells on the other. To analyse the distribution of leukocytes, distinct cell compartments as well as cell neighbourhood areas were defined. Finally, relative areal cell densities were calculated and these data were compared with those of an in vitro model of trophoblast invasion as well as with tissue fragments derived from decidua parietalis without trophoblast cells. MAIN RESULTS AND THE ROLE OF CHANCE: At first trimester placentation sites, a higher density of dNK cells as well as of dMph was found in close proximity to the invasive trophoblast (P ≤ 0.01), compared with the average areal cell density of decidual leukocytes in the tissue with exclusion of the trophoblast. The highest areal cell density of leukocytes was determined up to a distance of 20 µm from the trophoblast cells, whereas in more distant regions it was even lower than average, indicating a migration of these leukocytes towards the trophoblast invasion front. In the three-dimensional co-culture model, however, we found an enrichment of dMph (P ≤ 0.01) but not of dNK cells (P > 0,05) in the neighbourhood of the invasive trophoblast. LIMITATIONS, REASONS FOR CAUTION: The morphometric image analysis depends on intense immunohistochemical staining that is free of background and cross-reactivity. WIDER IMPLICATIONS OF THE FINDINGS: The presented method will be useful not only for the investigation of recurrent miscarriage but also in the fields of tumour immunology and inflammation. STUDY FUNDING/COMPETING INTEREST(S): The study was supported by the European Commission (Network of Excellence 'The Control of Embryo Implantation (EMBIC)', FP6-512040, lead researcher: P.S.), and by the Franz Lanyar Foundation of the Medical University of Graz, Austria (Grant #347). None of the authors declared a conflict of interests.

Human trophoblast cells express the immunomodulator progesterone-induced blocking factor.

Progesterone-induced blocking factor (PIBF) is an immunomoduatory factor with anti-abortive properties. In this study, we present evidence that PIBF is synthesized in the human placenta and determine its cellular source. Expression of PIBF was analysed with polyclonal rabbit anti-human PIBF antibodies against recombinant N-terminal 48kDa PIBF in first trimester and term placental tissues and in the choriocarcinoma cell line JAR by means of immunohistochemistry, confocal laser scanning microscopy of double immunofluorescence labelling, and Western blotting; RT-PCR was performed for analysis of PIBF mRNA in isolated trophoblast cells. PIBF protein is present in human first trimester and term placenta. Double immunofluorescence labelling localised PIBF to the extravillous cytotrophoblast. PIBF is also expressed heterogeneously by syncytiotrophoblast and part of the villous cytotrophoblast. Full-length PIBF mRNA encoded by exons 1-18 is present in isolated first trimester and term villous trophoblast and in the choriocarcinoma cell line JAR. The corresponding 90kDa protein is expressed by JAR cells, first trimester and term villous trophoblast cells. In addition, these cells express PIBF proteins of 50 and 34kDa. Trophoblast is a source of PIBF; its tissue distribution suggests a role both in systemic and local (decidual) immunoregulation.

Trophoblastic invasion in vitro and in vivo: similarities and differences.

BACKGROUND: The basic mechanisms of trophoblast invasion are not completely understood. This may be due to the lack of suitable in vitro models which enable experimental modulation of this complex process. In the present study, a three-dimensional co-culture model is used for comparing two factors considered to be implicated in the regulation of trophoblast invasion, the expression of HLA-G and apoptosis, in vitro and in vivo. METHODS: Tissue fragments from human first trimester decidua parietalis were put in close contact with spheroids of AC-1M59 trophoblast/choriocarcinoma hybrid cells as a model of the invasive trophoblast. Cryostat sections from these co-cultures were immunohistochemically stained and compared with first trimester placentation sites in vivo. RESULTS: Only the invasive trophoblast-derived cells showed an intensive staining for HLA-G, whereas the cells on the periphery of the confrontation culture exhibited only a weak staining. A similar staining pattern was found in vivo. Both in vitro and in vivo CD45(+) apoptotic leukocytes were frequently detected in close proximity to the invasive trophoblastic cells. CONCLUSIONS: In this co-culture system, key factors considered to be implicated in trophoblast invasion in vivo can also be demonstrated in vitro. Therefore, it may help in finding strategies for the management of diseases associated with deficient trophoblast invasion.

Apoptosis affects integration frequency: adult stem cells injected in blastocysts show high caspase-3 activity.

Chimeric organisms are commonly generated by injecting stem cells into blastocysts. Embryonic stem cells injected into the blastocoel cavity participate in the further development of the embryo. Adult stem cells have also been used in injection experiments to study their potential plasticity. In this study we focused on the early fate of injected human adult hematopoietic stem cells (HSCs). HSCs were followed immunohistochemically 1-19 h after injection into murine blastocysts. We found that they only rarely attached and integrated into the blastocysts. The high rate of loss of injected cells after prolonged in vitro culture of the chimeras can be explained by apoptosis. Our findings are consistent with previous studies reporting a low rate of integration of adult cells injected to produce chimeric embryos, but this is the first demonstration that the low efficiency of adult stem cell injections into blastocysts is influenced by apoptosis.

Insulin control of placental gene expression shifts from mother to foetus over the course of pregnancy.

AIMS/HYPOTHESIS: The human placenta is a complex organ situated at the interface between mother and foetus that separates maternal from foetal blood. The placental surfaces exposed to the two bloodstreams are different, i.e. trophoblasts and endothelial cells are in contact with the maternal and foetal circulation, respectively. Both cell types produce high insulin receptor levels. The aim of the present study was to test the hypothesis that spatio-temporal changes in insulin receptor expression in trophoblasts from first trimester to the endothelium at term shift the control of insulin-dependent processes from mother to foetus. METHODS: Global microarray analysis of primary trophoblasts from first trimester and term human placentas and endothelial cells from term human placentas cultured under hyperinsulinaemic and control conditions identified different sets of regulated genes in trophoblasts and endothelial cells. RESULTS: Insulin effects on placental gene expression underwent developmental changes from trophoblasts in the first trimester to endothelial cells at term that were paralleled by changes in levels of activated insulin receptors. The changes in gene regulation were both quantitative (i.e. magnitude of effect) and qualitative (i.e. specific genes affected and direction of regulation). CONCLUSIONS/INTERPRETATION: This spatio-temporal shift in insulin sensitivity throughout pregnancy allows maternal and foetal insulin to regulate different processes within the placenta at different gestational stages, facilitated by compartmentalisation of the insulin response. Thus, by altering the levels and function of insulin receptors in space and time, control of insulin-dependent processes in the human placenta will change from mother to foetus throughout gestation. This will be of particular interest in conditions associated with altered maternal or foetal insulin levels, i.e. diabetes mellitus or intrauterine growth restriction.

The soluble pool of HLA-G produced by human trophoblasts does not include detectable levels of the intron 4-containing HLA-G5 and HLA-G6 isoforms.

In the context of implantation and pregnancy, several immunomodulating functions have been attributed to the different HLA-G isoforms. Increasing attention is now being addressed to the actively secreted soluble forms, because they might have a systemic function or could be useful as diagnostic tools. However, the cellular source of secretion, even during pregnancy, where HLA-G expression level is known to be highest, is still under debate. To elucidate the conflicting results, we investigated the isoform distribution in human first trimester and term placentas in situ and in vitro. Results obtained by applying immunohistochemistry, western blot, enzyme-linked immunosorbent assay (ELISA) and RT-PCR show that (1) all of the alpha1 domain-containing HLA-G isoforms are restrictedly expressed in the extravillous cytotrophoblasts (EVCTs) and very few first-trimester syncytiotrophoblasts, which directly cover cell columns, whereas mesenchymal cells of the villous chorion do not express HLA-G; (2) as demonstrated in western blots, trophoblasts express only the HLA-G1 isoform; (3) HLA-G5 and -G6 transcripts could be detected in human term placenta and isolated first-trimester trophoblasts but levels are extremely low; and (4) conditioned media of primary first-trimester trophoblasts, and the chorion laeve-derived trophoblastic cell line AC1-M59 do contain HLA-G1 fragments shed from the cell surface. Our data provide substantial evidence that none of the intron 4-containing isoforms, the so-called actively secreted, soluble HLA-G5 or -G6, are produced by human trophoblasts in situ or in vitro.

Paraffin-embedded manipulated blastocysts: a tool to demonstrate stem cell plasticity?

One of the big question marks in current stem cell research is whether there is true plasticity of adult progenitor cells (APC) or if cell fusion is the principle source of the supposed plasticity. The generation of chimeras by injecting adult progenitor cells into blastocysts is not new. This paper describes an efficient embedding technique for murine blastocysts injected with human APC. This method could help in establishing a novel tool to analyse the process of plasticity, if it truly exists. If this is the case, this technology could be of great help to characterize surface markers of stem cells in great detail. On the other hand, fusion of cells could also be investigated. A system of embedding blastocysts was set up using paraffin for further analysis by means of light microscopy and immunohistochemistry. The embedding of the chimaeras consists of fixing them first with paraformaldehyde in phosphate-buffered saline (PFA/PBS), embedding them in gelatine, fixing the gelatine block with PFA/PBS and finally fixing the gelatine block in a Petri dish by embedding it in paraffin. Using this protocol, the morphology of the blastocysts is well preserved.

Expression of insulin, insulin-like growth factor I and glucocorticoid receptor in rat uterus and embryo during decidualization, implantation and organogenesis.

The significance of insulin, insulin-like growth factor I (IGF-I) and glucocorticoids to the early mammalian embryo is clear in that they are key regulators of both mitogenic and metabolic effects during development. In the present study, the temporal sequence of expression of the respective receptor proteins was investigated for the first time in the developing rat utero-embryonic unit between conception and day 12 of gestation using immunocytochemistry. Insulin, IGF-I and glucocorticoid receptor were expressed in embryonic tissues after the start of implantation, and were co-localized in the primary ectoderm, extraembryonic ectoderm as well as in the ectoplacental cone. The parietal endoderm was devoid of glucocorticoid receptor staining, whereas IGF-I receptor was absent in visceral endoderm. After completion of basic organogenesis, the neural tube, notochord, otic placode, Wolffian duct, mesonephros and intestinal tube expressed insulin, IGF-I and glucocorticoid receptor. The glucocorticoid receptor was not expressed in heart tube and dorsal aortae. Considerable amounts of insulin receptor were detected in trophoblast-derived giant cells. In the uterus, luminal epithelium, endometrial stromal and myometrial smooth muscle cells immunoreacted with antisera against insulin, IGF-I and glucocorticoid receptor. Endometrial glands remained negative for the glucocorticoid receptor throughout the gestational period investigated. Uterine hormone receptor expression reached a peak at days 4 and 5 of gestation in endometrial stromal cells and decidua, respectively. In conclusion, the demonstrated ontogenetic pattern of insulin, IGF-I and glucocorticoid receptor expression indicates the potential sites of biological action of the respective ligands, providing supportive evidence for their critical importance during the course of embryogenesis in rats.

Sustained hypoglycemia affects glucose transporter expression of human blood leukocytes.

The scarce data available on leukocyte glucose transporter expression are contradictory and nothing is known about its regulation by glycemic state. Therefore, cytospin preparations of blood leukocytes were searched immunocytochemically for the high-affinity glucose transporters GLUT1, 3, and 4. Hypoglycemia-associated quantitative changes in transporter expression were assessed by flow cytometry. Granulocytes and monocytes stained for GLUT1, 3, and 4. Granulocyte GLUT4 levels were increased by 73% (P < 0.05) under hypoglycemic conditions, which was paralleled by a reduction in GLUT1 and a rise in GLUT3. In monocytes, GLUT3 was elevated by 134% (P < 0.05), whereas GLUT1 and GLUT4 remained unaffected upon hypoglycemia. Apart from a minor subpopulation, lymphocytes were negative for these carriers. In conclusion, GLUT1, 3, and 4 are abundantly expressed in granulocytes and monocytes. The differential response of individual isoforms to hypoglycemia may represent a mechanism to protect the cells from the stress of glucose deprivation.

Localization of indoleamine 2,3-dioxygenase in human female reproductive organs and the placenta.

Indoleamine 2,3-dioxygenase (IDO) has been implicated in regulation of feto-maternal tolerance and protection against intracellular and extracellular pathogens. We have studied the expression of IDO in the human female reproductive tract and the placenta by immunohistochemistry. Endometrial glandular and surface epithelial cells showed increasing IDO expression during the course of the menstrual cycle. In term placenta, IDO was irregularly localized to the mesenchymal core and found in isolated areas of the syncytiotrophoblast. In first trimester pregnancy, IDO was not present in placental villi, but was present in glandular epithelium of the decidua, and there were distinctly positive cells scattered in the connective tissue, sometimes in conjunction with lymphoid aggregates. The endothelium of spiral arteries and of capillaries showed some, albeit no generalized, reactivity. IDO was also present in the epithelium of cervical glands and of Fallopian tubes. Specificity of antibody binding was confirmed by Western blot analysis. IDO mRNA was detected in first trimester decidua as determined by RT-PCR. IDO is secreted, as determined by analysis of cervical mucus by high pressure liquid chromatography for the presence of the tryptophan metabolite L-kynurenine, indicating IDO activity. Our results support the concept of IDO providing a mechanism of innate immunity protecting against ascending infections in the female reproductive tract.

HLA Class I protein expression in the human placenta.

The maternal tolerance to the semiallogeneic fetus is still a central theme in reproductive immunology. During placentation, fetally-derived, genetically dissimilar tissue and cells come into close contact with maternal tissue and cells, thus forming the so-called feto-maternal interface. The most extensive contact between fetally-derived and maternal blood cells is formed by the villous trophoblastic barrier, where the syncytiotrophoblast surface permanently floats in maternal blood. Further contact is made by some extravillous cytotrophoblast cells, either located at villous tips, in so-called cell islands, or the endovascular trophoblast population within the uteroplacental spiral arteries. The third contact zone is the so-called junctional zone within the decidua where the invading extravillous trophoblast cells encounter all maternal tissue leukocytes, which are mainly NK cells, macrophages and T cells; this junctional zone extends at the edge of the placenta to the amnio-chorionic membranes where the chorionic laeve trophoblast has intimate contact with decidua tissue. It is worth mentioning that evidence has shown that even in healthy pregnancies fetal and maternal lymphoid cells are able to transgress the trophoblastic barrier, which, anatomically, seems completely impermeable. Because of this intimate contact of foreign cells to the foreign immune system it is important to define the antigenic status of the placental cells, in particular with respect to antigens of the Major Histocompatibility complex. The role of the highly polymorphic classical class I molecules HLA -A, -B, -C, which are expressed on almost all somatic cells, is the induction of a specific immune response by presenting peptide antigens to T cells. In contrast, the non-classical HLA class I molecules HLA-G and HLA-E are thought to be involved in the induction of immune tolerance by acting as ligands for inhibitory receptors present on NK cells and macrophages. The non-classical HLA-E is also expressed ubiquitously, but HLA-G expression is characterized by a unique tissue expression mainly in the human placenta. A further feature of HLA-G is that its mRNA has undergone alternative splicing, resulting in at least 6 different isoforms, encoding different proteins: 4 membrane-bound and 2 soluble forms, which could simultaneously maintain different functions depending on their molecular structure. In our immunohistochemical study we investigated the expression of classical and non-classical HLA class I proteins in human placenta using various mAbs, which were kindly provided by the groups of A. Ziegler, D. Geraghty, O. Genbacev, MT. McMaster, A. King, YW. Loke and Ph. Le Bouteiller. For HLA-A,-B detection we used the antibody LA45; for detection of HLA-C,-B mAbs Tü149 and HC10. HLA-C expression alone was detected with mAb L31. HLA-G expression was studied using antibodies 4H84, G233, 87G, 16G1 and BFL.1. For HLA-E staining we used antibodies DT9 and V16. The classical HLA class I proteins are expressed in all non-trophoblastic cells including the fetal and maternal cells. Comparison of HLA-A and HLA-B staining intensities within the villous stroma indicates that during first trimester of pregnancy the fetal HLA-B proteins are expressed before HLA-A appears. Among the trophoblast populations, the syncytiotrophoblast does not show any HLA class I staining, but the extravillous cells express high amounts of HLA-G together with HLA-C. King and co-workers have shown recently, using methods other than immunohistochemistry, that first trimester extravillous trophoblast cells are also likely to express HLA-E. By contrast we did not detect HLA-E in any trophoblasts with antibodies DT9 and V16. There is still an ongoing and also controversial discussion about which kinds of cells in the placenta, other than extravillous trophoblast, express which kind of the HLA-G isoforms. Depending on the antibodies and the different immunohistochemical techniques used, different results have been described: Antibody 16G1 specific for soluble HLA-G labels syncytiotrophoblast, antibody BFL.1 endothelial cells of chorionic fetal blood vessels and antibody 87G Hofbauer cells. All these HLA-G labelings, apart from extravillous trophoblasts, are in complete contrast to the reaction pattern (merely extravillous trophoblast) given by antibody 4H84, which recognizes all HLA-G isoforms -including the soluble ones- through an epitope located on the a 1-domain of HLA-G. Future studies employing isoform-specific antibodies, which are not yet available for all of the possible isoforms, will elucidate the function and expression pattern of HLA-G in the human placenta.

From maternal glucose to fetal glycogen: expression of key regulators in the human placenta.

The present study investigated the expression of glycogenin, the protein primer for glycogen synthesis, and the high affinity glucose transporter isoform GLUT3 as a further potential regulator of cellular glycogen metabolism, in first trimester and term human placenta using immunohistochemistry and Western blotting. At term, glycogenin was most abundant in the endothelium of fetal vessels. Trophoblast as well as basal decidual cells were moderately stained. The glycogenin distribution pattern in first trimester placentae resembled that at term, but reactivity was generally less intense. Extravillous trophoblast and villous cytotrophoblast were the major sites of GLUT3 expression. Endothelial cells were also strongly labelled with the GLUT3 antiserum. Western blotting identified both free and glucosylated glycogenin, as well as a 48 kDa band reacting with GLUT3 antiserum in placental villous tissue. Glycogenin immunoreactivity remained unaffected by amylolytic glycogen digestion, although preceding electron microscopical examination demonstrated the presence of glycogen. These data may indicate that placental glycogenin can be recycled from the immature glycogen or that it is located on the surface of the glycogen molecule. In conclusion, the co-expression of glycogenin with GLUT3 might enable glycogen-storing cells to exchange glucose quite effectively according to prevailing metabolic demands of glycogen synthesis or degradation.

Prooxidant activity of melatonin promotes fas-induced cell death in human leukemic Jurkat cells.

The antioxidant activity of melatonin (MEL) has been considered to constitute part of its physiological as well as pharmacological effects. However, as described herein we found a profound prooxidant activity of micro- to millimolar concentrations of MEL in the human leukemic Jurkat cell line. This prooxidant effect was increased in glutathione-depleted cells and counteracted by antioxidants. As a consequence MEL promoted fas-induced cell death. These data therefore indicate that MEL may be a modulator of the cellular redox status, but does not necessarily act as an intracellular antioxidant.

Glucose transporter expression in rat embryo and uterus during decidualization, implantation, and early postimplantation.

Efficient transfer of glucose from the mother to the embryonic compartment is crucial to sustain the survival and normal development of the embryo in utero, because the embryo's production of this primary substrate for oxidative metabolism is minimal. In the present study, the temporal sequence of expression of the sodium-independent facilitative glucose transporter isoforms GLUTs 1, 3, 4, and 5 was investigated in the developing rat uteroembryonic unit between conception and Gestational Day 8 using immunohistochemistry. The GLUTs 1, 3, and 4 were expressed in the embryonic tissues after the start of implantation, being colocalized in the parietal endoderm, visceral endoderm, primary ectoderm, extraembryonic ectoderm, and the ectoplacental cone. In the uterus, a faint GLUT1 labeling emerged, but not until Gestational Day 3, in the luminal epithelium, endometrial stroma, and decidual cells. The intensity of GLUT1 staining increased in the latter population with progressing decidualization. Endometrial glands and myometrial smooth muscle cells stained neither for GLUT1 nor for GLUT3 until postimplantation. During all developmental stages examined, GLUT4 was visualized throughout the pregnant rat uterus, as was GLUT3 (with the above-mentioned exceptions). The density of GLUT5 was generally less than the sensitivity of the immunohistochemical detection method in all tissues investigated. In conclusion, the data point to a significant expression of the high-affinity glucose transporters GLUTs 1, 3, and 4 in the rat uteroembryonic unit, providing supportive evidence for an important role of facilitative glucose diffusion during peri-implantation development.

Uterine natural killer cells in a three-dimensional tissue culture model to study trophoblast invasion.

The high numbers of CD56(+) cells with natural killer (NK) functions present in the uterine mucosa during the late secretory phase of the menstrual cycle and during early pregnancy have been considered to be implicated in implantation and in the regulation of trophoblast invasion. A three-dimensional organ culture model was used to study the interactions of these uterine NK cells with Jeg-3 and BeWo choriocarcinoma cells as a model of the invasive trophoblast. For this purpose, fragments of endometrial and decidual tissue were put in close contact with multicellular spheroids of choriocarcinoma cells in small silicon funnels. After the formation of stable contacts, the confrontation cultures were transferred to spinner flasks, cultivated for up to 6 days, and prepared for immunohistochemistry. During 2 days of cocultivation, the first cells started to move forward into the stromal component of the confrontation culture as demonstrated by staining of the choriocarcinoma cells using anti-human cytokeratin. Invasion advanced until, after a total of 6 days, some choriocarcinoma cells had already penetrated deeply into the host tissue. After a cultivation period of 1 week, both the endometrial and decidual tissue fragments still contained several CD56(+) uterine NK cells, and some of them expressed the proliferation-associated marker Ki-67 without any exogenous activation. A few CD56(+) cells were found directly at the invasion front, as well as between the choriocarcinoma cells. These cells also contained the cytolytic granule protein perforin indicating a migration of NK cells with cytolytic potential toward the potentially invasive cells. In conclusion, this human system closely resembles the in vivo conditions during trophoblast invasion and provides an appropriate in vitro model for studying dynamic processes involving various cell types during trophoblast invasion at the experimental level. Moreover, it enables us to study the effects of cytokines and growth factors that possibly regulate trophoblast invasion.

Role of various tissues in apo(a) fragmentation and excretion of fragments by the kidney.

BACKGROUND: Lipoprotein(a) [Lp(a)] is an atherothrombotic plasma lipoprotein with unknown function. Little is known about the catabolism of this lipoprotein, in particular the steps related to apolipoprotein(a) [apo(a)] fragmentation and excretion by the kidney. MATERIAL AND METHODS: High plasma levels (up to 9 mg dL(-1)) of the N-terminal fragment of apo(a) were expressed in mice by adenovirus mediated gene transfer. Plasma of such N-apo(a) mice was injected into acceptor mice and the fragmentation and urinary secretion of N-apo(a) were followed by immunochemical techniques. RESULTS: Mice transduced with N-Ad expressed apo(a)-fragments with 3-11 kringle-IV (KIV) repeats. Injection of N-apo(a)-plasma from donor mice into acceptor mice resulted in fragmentation of N-apo(a)s with 3-11 KIVs yielding smaller peptides down to 2 KIVs. Secretion of N-apo(a)-fragments with 2 to maximally 6 KIVs into urine occurred as early as 2 min after injection. Immunohistochemical studies of kidney suggested filtration as a mechanism of apo(a)-fragment excretion. When N-apo(a) was incubated in vitro with various tissues from perfused mice, skeletal muscle and kidney followed by liver and spleen contributed to fragmentation. Tissues from unperfused organs, or the addition of normal mouse plasma, caused marked reduction in N-apo(a) fragmentation. EDTA, and not aprotinin or leupeptin, prevented apo(a) cleavage. CONCLUSION: Here we provide evidence that apo(a) is cleaved by metalloproteinases located on skeletal muscle, kidney and other organs. Small apo(a)-fragments up to a size of 6 KIVs are excreted into urine, yet a major portion of apo(a) fragments is removed from circulation extrarenally.