Biomedical subjects

M Krieger

Publications and source records attributed to M Krieger.

At least 55 records · Page 3Linked to original sources

PubMed1997

Isolation and characterization of ovine tyrosine hydroxylase mRNA.

Tyrosine hydroxylase (TH) cDNA has been characterized in rodents and primates, but only a few studies have been developed in ungulates, except in cows. Because sheep is a species used for many physiological studies, it was of interest to clone TH cDNA in this species. Ovine TH cDNA was purified from a library of sheep adrenal glands. The entire cDNA was 1,721 bp long. It presented a higher percentage of similarity with bovine TH cDNA (93%) than with rodent cDNAs (75%). The deduced amino acid sequence was 490 amino acids long and had 96% similarity with the bovine amino acid sequence. The entire cDNA and different fragments obtained with endonuclease restriction enzymes were cloned in plasmid pUC 18 and were labeled with 35S-dATP to detect TH mRNA by in situ hybridization. Strong labelings were observed on adrenal medulla and on noradrenergic and dopaminergic neurons in the sheep but also in the cow and pig. This labeling matched completely TH immunohistochemical staining obtained on the same sections with anti-TH antibodies. Ovine TH cDNA is a useful tool to study the variations of TH mRNA levels in sheep catecholaminergic neurons.

Amino Acid Sequence↗

PubMed1997

Scavenger receptor BI--a cell surface receptor for high density lipoprotein.

The receptor-mediated transfer of lipids between cells and lipoproteins plays an important role in lipoprotein metabolism and cardiovascular disease. Although there have been many valuable studies of HDL binding to tissues, cells and membranes, and of the potential role of such binding in the transport of lipids between HDL and cells, much less is known about HDL receptors than about receptors for other lipoproteins (e.g. LDL, chylomicrons, vitellogenin). Here we review recent studies of the class B, type I scavenger receptor, which appears to be a physiologically relevant, cell surface HDL receptor that mediates the selective uptake of lipids by cells.

Animals↗

PubMed1997

The other side of scavenger receptors: pattern recognition for host defense.

Scavenger receptors bind modified lipoproteins and may play an important role both in normal and in pathological lipid metabolism. A number of different classes of scavenger receptors have been identified and several of these are multiligand receptors. Studies, both in vitro and in vivo, have indicated that at least some of these scavenger receptors may serve as pattern recognition receptors because they are able to bind a wide variety of pathogens. As a consequence, they may play key roles in innate immunity and host defense.

Animals↗

PubMed1997

Apolipoproteins of HDL can directly mediate binding to the scavenger receptor SR-BI, an HDL receptor that mediates selective lipid uptake.

The class B type I scavenger receptor, SR-BI, binds HDL, mediates selective uptake of HDL cholesteryl esters by cultured cells, and its expression is coordinately regulated with steroidogenesis in several endocrine tissues (adrenal, ovary, testes). SR-BI can also bind LDL and anionic phospholipids, which raised the possibility that HDL apolipoproteins might not participate directly in HDL binding. We have examined the ability of individual human HDL apolipoproteins (apoA-I, apoA-II, and apoC-III) reconstituted into phospholipid/unesterified cholesterol complexes to bind to murine SR-BI (mSR-BI) expressed in stably transfected cultured cells. All three apolipoprotein/phospholipid/unesterified cholesterol complexes specifically associated with mSR-BI expressing cells with high affinity and competed for the binding of HDL, while apolipoprotein-free complexes did not. Furthermore, lipid-free forms of these soluble apolipoproteins also competed for HDL and apolipoprotein/ phospholipid/cholesterol complex association with mSR-BI, but locust high density lipophorin and bovine serum albumin were not effective competitors.Thus, all three of the HDL apolipoproteins (apoA-I, apoA-II, and apoC-III) tested can directly mediate binding to mSR-BI, and this multiligand apolipoprotein receptor may be responsible for at least some of the multilipoprotein and apolipoprotein binding activity previously observed in cells and tissues.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1996

Regulation by adrenocorticotropic hormone of the in vivo expression of scavenger receptor class B type I (SR-BI), a high density lipoprotein receptor, in steroidogenic cells of the murine adrenal gland.

The class B, type I scavenger receptor, SR-BI, binds high density lipoprotein (HDL) and can mediate selective uptake of HDL cholesteryl esters by cultured cells. The high levels of expression of SR-BI in steroidogenic tissues and the importance of selective uptake from HDL as a source of cholesterol for steroidogenesis raised the possibility that SR-BI may participate in cholesterol delivery to steroidogenic tissues in vivo. We have used immunoblotting and immunohistochemical methods to show that SR-BI is specifically expressed in a distinctive pattern on the surfaces of steroid-producing cells in the murine adrenal gland's cortex and that its expression in vivo is induced by adrenocorticotropic hormone and suppressed by glucocorticoids. Thus, expression of SR-BI protein is coordinately regulated with adrenal steroidogenesis. These data provide strong support for the hypothesis that SR-BI is a physiologically relevant HDL receptor that provides substrate cholesterol for steroid hormone synthesis.

Adrenal Glands↗

PubMed1996

Structures of class A macrophage scavenger receptors. Electron microscopic study of flexible, multidomain, fibrous proteins and determination of the disulfide bond pattern of the scavenger receptor cysteine-rich domain.

Structures of secreted forms of the human type I and II class A macrophage scavenger receptors were studied using biochemical and biophysical methods. Proteolytic analysis was used to determine the intramolecular disulfide bonds in the type I-specific scavenger receptor cysteine-rich (SRCR) domain: Cys2-Cys7, Cys3-Cys8, and Cys5-Cys6. This pattern is likely to be shared by the highly homologous domains in the many other members of the SRCR domain superfamily. Electron microscopy using rotary shadowing and negative staining showed that the type I and II receptors are extended molecules whose contour lengths are approximately 440 A. They comprised two adjacent fibrous segments, an alpha-helical coiled-coil ( approximately 230 A, including a contribution from the N-terminal spacer domain) and a collagenous triple helix ( approximately 210 A). The type I molecules also contained a C-terminal globular structure ( approximately 58 x 76 A) composed of three SRCR domains. The fibrous domains were joined by an extremely flexible hinge. The angle between these domains varied from 0 to 180 degrees and depended on the conditions of sample preparation. Unexpectedly, at physiologic pH, the prevalent angle seen using rotary shadowing was 0 degrees , resulting in a structure that is significantly more compact than previously suggested. The apparent juxtaposition of the fibrous domains at neutral pH provides a framework for future structure-function studies of these unusual multiligand receptors.

Amino Acid Sequence↗

PubMed1996

Regulation of scavenger receptor, class B, type I, a high density lipoprotein receptor, in liver and steroidogenic tissues of the rat.

The scavenger receptor, class B, type I (SR-BI) binds HDL and mediates the selective transfer of cholesteryl esters from HDL to cultured cells. The tissue distribution of SR-BI in mice suggests that this receptor may deliver HDL-cholesterol to the liver and to nonplacental steroidogenic tissues. To examine the role of SR-BI in vivo, we determined its tissue and cell type-specific expression pattern and regulation in rats. High levels of immunodetectable SR-BI were present in the adrenal gland, ovary, and liver. In pregnant animals, the mammary gland also expressed high levels of the protein. SR-BI was localized by immunofluorescence to the surfaces of steroidogenic cells in the zona fasciculata and zona reticularis of the adrenal gland and to the corpus luteal cells of the ovary. High-dose estrogen treatment dramatically reduced SR-BI in the liver and increased SR-BI in the adrenal gland and corpus luteal cells of the ovary. These estrogen-induced increases in SR-BI in the adrenal gland and ovary were accompanied by enhanced in vivo uptake of fluorescent lipid from HDL. The administration of human chorionic gonadotropin induced a dramatic increase in SR-BI in the steroidogenic Leydig cells of the testes. These findings suggest that SR-BI mediates physiologically relevant uptake of cholesterol from HDL to nonplacental steroidogenic tissues in vivo.

Adrenal Glands↗

PubMed1996

A single point mutation in epsilon-COP results in temperature-sensitive, lethal defects in membrane transport in a Chinese hamster ovary cell mutant.

At the nonpermissive temperature of 39.5 degrees C, the Chinese hamster ovary cell conditionally lethal, temperature-sensitive (ts) mutant ldlF exhibits the following defects: rapid degradation of low density lipoprotein receptors, disruption of ER-through Golgi transport, and disintegration of the Golgi apparatus. All of these are corrected by transfection with an expression vector for wild-type epsilon-COP, a subunit of coatomers (Guo, Q., Vasile, E., and Krieger, M. (1994) J. Cell Biol. 125, 1213-1224). We now report the identification in ldlF cells of a point mutation in the epsilon-COP gene, Glu251 to Lys251, which prevents the corresponding cDNA from correcting the defects in transfected ldlF cells and the immunochemical analysis of the synthesis, structure, and stability of epsilon-COP. At the permissive temperature (34 degrees C), the steady state level of ts-epsilon-COP in ldlF cells was about half that of epsilon-COP in wild-type Chinese hamster ovary cells and the isoelectric point of ts-epsilon-COP was 0.14 pH units higher than that of the wild-type protein. The stability but not the biosynthesis of ts-epsilon-COP was temperature-sensitive (t1/2 > 6 h at 34 degrees C and approximately 1-2 h at 39.5 degrees C), and this accounts for the virtual absence of detectable ts-epsilon-COP protein in ldlF cells after incubation at 39.5 degrees C for > 6h. The steady state levels in ldlF cells of another coatomer subunit, beta-COP, and the peripheral Golgi protein ldlCp were not temperature-sensitive. Thus, a mutation in epsilon-COP that causes instability at 39.5 degrees C is responsible for all of the temperature-sensitive defects in ldlF cells, and the stability of beta-COP is not linked directly to that of epsilon-COP. ldlF cells should be useful for the future analysis of the structure and function of epsilon-COP, the assembly of COPs into coatomers, and the participation of coatomers in intracellular membrane transport.

Amino Acid Sequence↗

PubMed1996

Progesterone receptor immunoreactivity in aromatic L-amino acid decarboxylase-containing neurons of the guinea pig hypothalamus and preoptic area.

A double-labeling immunofluorescence procedure was used to determine whether progesterone receptor (PR)-immunoreactive (IR) neurons in the preoptic area and hypothalamus of female guinea pigs also contained aromatic L-amino acid decarboxylase (AADC), an enzyme involved in the synthesis of both catecholamines and serotonin. Immunostaining was performed on cryostat sections prepared from ovariectomized guinea pigs primed by estradiol to induce PR. The nuclear presence of PR was visualized by a red fluorescence while the AADC-containing perikarya showed a yellow-green fluorescence. The topographic distribution of AADC-IR neurons was investigated by using a specific antiserum obtained by immunization of rabbits with a recombinant protein beta-galactosidase-AADC in the two regions known to contain the densest populations of estradiol-induced PR-IR cells: the preoptic area and the mediobasal hypothalamus. The localization of PR-IR and AADC-IR cell populations showed considerable overlap in these areas, mainly in the medial and periventricular preoptic nuclei and in the arcuate nucleus. A quantitative analysis of double-labeled cells estimated that about 15% to 23% of AADC-IR cells in the preoptic area and about 11% to 21% of AADC-IR cells in the arcuate nucleus possessed PR. This colocalization persisted throughout the rostrocaudal extent of these areas and represented 3% to 9% of the population of PR-IR cells. These findings provide neuroanatomical evidence that a subset of AADC neurons is directly regulated by progesterone. The exact physiological role of this enzyme in target cells for progesterone is not understood. AADC may be involved in functions other than that for the synthesis of the classical neurotransmitters.

Animals↗

PubMed1996

Identification of scavenger receptor SR-BI as a high density lipoprotein receptor.

High density lipoprotein (HDL) and low density lipoprotein (LDL) are cholesterol transport particles whose plasma concentrations are directly (LDL) and inversely (HDL) correlated with risk for atherosclerosis. LDL catabolism involves cellular uptake and degradation of the entire particle by a well-characterized receptor. HDL, in contrast, selectively delivers its cholesterol, but not protein, to cells by unknown receptors. Here it is shown that the class B scavenger receptor SR-BI is an HDL receptor. SR-BI binds HDL with high affinity, is expressed primarily in liver and nonplacental steroidogenic tissues, and mediates selective cholesterol uptake by a mechanism distinct from the classic LDL receptor pathway.

Adrenal Glands↗

PubMed1996

Osteoneogenesis and its influencing factors during treatment with the Ilizarov method.

The radiographs of 57 patients who had undergone 58 callus distractions and 13 epiphyseal distractions were evaluated. During the course of treatment, the density of the distraction areas on radiographs was measured in total and along the medial, lateral, ventral, and dorsal margins using a digital radiograph processing system. The densities of the whole distraction length were correlated to the following parameters: age of patient, start of distraction after corticotomy, mean distraction speed, mean amount of weight load during the period of distraction and consolidation, location of corticotomy (distal femoral metaphysis versus the proximal tibial one), and diclofenac medication. Except for the location of corticotomy and the diclofenac medication, the density was influenced by all these parameters. Age of the patient and weight load were the most important parameters. Patients with leg shortening caused by poliomyelitis and a patient with a shortened leg after amniotic strangulation showed a slower rise of the density trend curve on radiographs than the other patients. When comparing the different regional density curves, a significant gradual density decrease could be observed from the medial to the lateral side in the femur, from lateral to medial in the tibia, and from the dorsal to the ventral side in both bones. The respective differences between lateral and medial density, and between dorsal and ventral density, were significantly higher in cases of callus distraction than in cases in which epiphyseal distraction had been used. The amount of bone regeneration varied regionally primarily because of the inhomogeneous soft tissue covering of the bone and the impairment of its local blood supply by the surgical exposure for the corticotomy. The clinical relevancy of the various parameters for osteoneogenesis is discussed in this article.

Adolescent↗

PubMed1995

A confocal approach to the morphofunctional characterization of the transient tyrosine hydroxylase system in the rat suprachiasmatic nucleus.

The suprachiasmatic nucleus (SCN) of the neonatal rat is transiently innervated by tyrosine hydroxylase (TH) fibers of unknown origin and whose catecholaminergic nature is rather doubtful. In order to characterize this system morphofunctionally, immunocytochemical double labelling and confocal laser scanning microscopy analysis were employed on cryostat brain sections of 10-day-old rats. Simultaneous stainings for neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity showed that they are not colocalized, neither in the SCN fibers nor in the intergeniculate leaflet (IGL) neurons, site of origin of the NPY projection to the SCN. Therefore, the possibility that SCN transient TH fiber system originates from the IGL could be excluded. Double labelling for TH and aromatic L-aminoacid decarboxylase (AADC) demonstrated that transient SCN TH immunoreactive (IR) fibers are AADC negative, thus supporting the hypothesis of their non-catecholaminergic nature. Moreover two new group of cells which are TH positive and AADC negative were found: one in the SCN and the other in the periventricular hypothalamic nucleus (PHN). The presence of somatostatin (SRIF) and TH in PHN neurons and SCN fibers suggested their possible colocalization, but double immunolabellings gave negative results. Simultaneous immunocytochemical staining for vasoactive intestinal polypeptide (VIP) and TH showed that TH fibers may interact with ventrolateral SCN VIP neurons. This result suggests a possible involvement of TH fibers in regulating VIP cells activity in the entrainment of circadian rhythms.

Animals↗

PubMed1995

The class B scavenger receptors SR-BI and CD36 are receptors for anionic phospholipids.

The specific recognition of anionic phospholipids in the outer leaflets of cell membranes and lipoproteins by cell surface receptors may play an important role in a variety of physiologic and pathophysiologic processes (e.g. recognition of damaged or senescent cells by the reticuloendothelial system or lipoprotein homeostasis). Several investigators have described anionic phospholipid binding to cells, and phosphatidylserine (PS) binding to a partially purified approximately 95-kDa membrane protein has recently been reported (Sambrano, G.R., and Steinberg, D. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 1396-1400). Using both direct binding and ligand competition assays in transfected cells, we have found that two class B scavenger receptors, SR-BI and CD36, can tightly bind PS and phosphatidylinositol (PI)-containing liposomes (Kd for PS liposome binding to SR-BI is approximately 15 micrograms phospholipid/ml or 0.18 nM (mol PS liposomes/l), but not phosphatidylcholine, phosphatidylethanolamine, or sphingomyelin liposomes. PS and PI liposomes, but not the others, could effectively compete with PS liposomes and modified or native lipoproteins for binding to these receptors. Phosphatidic acid, another anionic phospholipid, could also compete, but was not as effective as PS or PI. Class B scavenger receptors are the first molecularly well-defined, specific cell surface receptors for anionic phospholipids to be described.

Animals↗

PubMed1995

Expression cloning of dSR-CI, a class C macrophage-specific scavenger receptor from Drosophila melanogaster.

Mammalian class A macrophage-specific scavenger receptors (SR-A) exhibit unusually broad binding specificity for a wide variety of polyanionic ligands. The properties of these receptors suggest that they may be involved in atherosclerosis and host defense. We have previously observed a similar receptor activity in Drosophila melanogaster embryonic macrophages and in the Drosophila macrophage-like Schneider L2 cell line. Expression cloning was used to isolate from L2 cells a cDNA that encodes a third class (class C) of scavenger receptor, Drosophila SR-CI (dSR-CI). dSR-CI expression was restricted to macrophages/hemocytes during embryonic development. When expressed in mammalian cells, dSR-CI exhibited high affinity and saturable binding of 125I-labeled acetylated low density lipoprotein and mediated its chloroquine-dependent, presumably lysosomal, degradation. Although the broad polyanionic ligand-binding specificity of dSR-CI was similar to that of SR-A, their predicted protein sequences are not similar. dSR-CI is a 609-residue type I integral membrane protein containing several well-known sequence motifs, including two complement control protein (CCP) domains and somatomedin B, MAM, and mucin-like domains. Macrophage scavenger receptors apparently mediate important, well-conserved functions and may be pattern-recognition receptors that arose early in the evolution of host-defense mechanisms. Genetic and physiologic analysis of dSR-CI function in Drosophila should provide further insights into the roles played by scavenger receptors in host defense and development.

Amino Acid Sequence↗

PubMed1995

Randomized controlled trial of Ringer solution versus serum for partial exchange transfusion in neonatal polycythaemia.

UNLABELLED: We tested whether crystalliod solutions could be used instead of colloid solutions for partial exchange transfusions (PET) in polycythaemic neonates because crystalloid solutions are cheap, carry no risk of anaphylactic reactions and can be sterilized. We randomly assigned 20 term neonates with venous haematocrit (Hct) > 0.65 l/l to PET with either a serum preparation (BISEKO) or Ringer solution. Plasma volume (PV) was measured with Evans blue dilution. Blood volume (BV) and red cell mass were calculated from PV and venous Hct. Before PET both serum and Ringer groups had the same Hct (0.69 (0.66-0.76) vs 0.69 (0.66-0.71) l/l; median (range)) and BV (108 (81-116) versus 96 (68-121) ml/kg. During PET an equivalent amount of blood was withdrawn stepwise (19 (14-26) versus 17 (13-25) ml/kg and replaced by either serum or Ringer solution. More of the Ringer solution (median 77%) than of the serum (median 36%) given left the intravascular space within 4 h after PET (P = 0.016); but there was no significant difference in Hct after Ringer-PET compared to serum-PET (median 0.58 vs 0.56 l/l). No infant required repeat PET. Ringer-PET reduced BV from high to normal values (from median 96 to 83 ml/kg; P = 0.005), whereas after serum-PET BV remained high (from median 108 to 98 ml/kg; not significant). CONCLUSION: PET with Ringer solution resulted in a haemodilution comparable to PET with serum and a correction of hypervolaemia.

Blood Component Transfusion↗

PubMed1995

[Possible applications of ultrasound in corticotomy-callus distraction].

Sonographic examination can yield additional information in the course of corticotomy-callus distraction. Hence, we focus on individual slices--which are different from the standardised ultrasound examination of the skeleton system--in the area of the corticotomy-callus distraction. In ultrasound examination the structure of corticalis in the field of corticotomy is scanned circularly. Depending on the point of time of the corticotomy between the structure of corticalis, the callus can be visualised sonographically. The callus distraction can be divided into three stages: I. echo-poor structure between the two ends of the corticalis, II. echo-rich structure between the two ends of the corticalis, III. area of corticalis in the area of distraction with (III a), visualised without (III b) break. The described method is an additional low-cost imaging procedure in diagnosis, for the patient free of radiation and stress, which can yield additional information during and after completed callus distraction (question of permissible emotional stress). The examination is reproducible. The x-ray-controls in the course of time are mandatory, because the sonographic examination cannot judge reliably the deviation of the axis in the area of callus distraction.

Adolescent↗

PubMed1995

[Factors affecting bone regeneration in Ilizarov callus distraction].

We evaluated the X-rays of 36 patients who underwent 50 callus distractions. With the aid of a computerized digitalisation system for analogue films, the relative X-ray density of the distraction area was calculated for each X-ray. These relative X-ray densities were figured graphically for the duration of treatment for each patient. In the consolidation phase, the graph of each patient had a logarithmic relationship. The gradients of the logarithmic density curves were considered an indicator of the quantity of new bone formation. These gradients were correlated to the following clinical parameters: age of the patient, beginning of distraction after corticotomy, average speed of distraction, average weight bearing during the distraction and consolidation phase, location of corticotomy (distal femur versus proximal tibia) and diclofenac medication. Except for the location of the corticotomy and diclofenac, all parameters had an influence on osteoneogenesis by callus distraction. The parameters affecting new bone formation the most were the age of the patient and weight bearing. Patients aged under 18 years (p = 0.005), beginning of distraction later than 8 days (p = 0.109), an average distraction speed below 1 mm/day (p = 0.079), and average weight bearing of more than 30 kg (p = 0.068 for the distraction phase and p = 0.089 for the consolidation phase) showed a quantitatively higher rate of new bone formation by callus distraction than the patients in the other groups. Patients with a shorter leg due to poliomyelitis and one patient with an amniotic leg tie showed a slower increase in X-ray density graphs than the other patients.

Absorptiometry, Photon↗

PubMed1994

Expression cloning of SR-BI, a CD36-related class B scavenger receptor.

Scavenger receptors are integral membrane proteins that mediate the endocytosis of modified lipoproteins. The first of these to be purified and cloned were the type I and II macrophage scavenger receptors (SR-AI and SR-AII; class A scavenger receptors). Subsequently, the cell surface protein CD36 was shown to bind oxidized low density lipoprotein (oxidized LDL). From a Chinese hamster ovary (CHO) cell variant we have cloned by expression the cDNA for a new member of the CD36 family of membrane proteins, SR-BI, whose predicted protein sequence of 509 amino acids is approximately 30% identical to those of the four previously identified family members. Both SR-BI and CD36 displayed high affinity binding for acetylated LDL with an apparent dissociation constant on the order of approximately 5 micrograms of protein/ml. The ligand binding specificities of CD36 and SR-BI, determined by direct binding or competition assays, were similar, but not identical; both bind modified proteins (acetylated LDL, oxidized LDL, maleylated bovine serum albumin), but not the broad array of other polyanions (e.g. fucoidin, polyguanosinic acid, carrageenan) which are ligands of the class A receptors. Thus, SR-BI and CD36 define a second class of scavenger receptors, designated class B. Native LDL, which does not bind to either class A receptors or CD36, unexpectedly bound with high affinity to SR-BI. Northern blot analysis of murine tissues showed that SR-BI was most abundantly expressed in fat and was present at moderate levels in lung and liver. Furthermore, SR-BI mRNA expression was induced upon differentiation of 3T3-L1 cells into adipocytes. Thus, the tissue distribution of expression and ligand binding properties of SR-BI raise the possibility that this cell surface receptor may play an important role in lipid metabolism.

Amino Acid Sequence↗