Critical assessment of paradigms in aging research.
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Aging↗
Biomedical subjects
H Gershon
Publications and source records attributed to H Gershon.
The budding yeast, Saccharomyces cerevisiae, as a model for aging research: a critical review.
In this review we discuss the yeast as a paradigm for the study of aging. The budding yeast Saccharomyces cerevisiae, which can proliferate in both haploid and diploid states, has been used extensively in aging research. The budding yeast divides asymmetrically to form a 'mother' cell and a bud. Two major approaches, 'budding life span' and 'stationary phase' have been used to determine 'senescence' and 'life span' in yeast. Discrepancies observed in metabolic behavior and longevity between cells studied by these two systems raise questions of how 'life span' in yeast is defined and measured. Added to this variability in experimental approach and results is the variety of yeast strains with different genetic make up used as 'wild type' and experimental organisms. Another problematic genetic point in the published studies on yeast is the use of both diploid and haploid strains. We discuss the inherent, advantageous attributes that make the yeast an attractive choice for modern biological research as well as certain pitfalls in the choice of this model for the study of aging. The significance of the purported roles of the Sir2 gene, histone deacetylases, gene silencing, rDNA circles and stress genes in determination of yeast 'life span' and aging is evaluated. The relationship between cultivation conditions and longevity are assessed. Discrepancies between the yeast and mammalian systems with regard to aging are pointed out. We discuss unresolved problems concerning the suitability of the budding yeast for the study of basic aging phenomena.
Aging↗
Paradigms in aging research: a critical review and assessment.
This is the first in a series of articles in which we intend to critically review some of the currently used models in gerontology research and evaluate their contribution to advancing our understanding of the phenomenon of senescence. The major theories of aging are considered. We discuss what makes a model useful in general and for aging research in particular. We suggest criteria for the selection of paradigms for the study of aging. The criteria we suggest for identifying underlying mechanisms that lead to age related changes are: intraspecies universality, intrinsicality, progressiveness, and interspecies universality. The subsequent articles of this series shall consider the merits and possible drawbacks of some of the most commonly used models of the biology of aging: (a) the yeast Saccharomyces cerevisiae; (b) the nematode, Caenorhabditis elegans and the fruitfly, Drosophila melanogaster; (c) mammalian cells in culture and telomerase model; (d) mitochondria and aging; (e) progeroid syndromes; (f) in vivo studies with laboratory rodent strains; and (g) plant senescence.
Aging↗
Receptors involved in the phagocytosis of senescent and diamide-oxidized human RBCs.
BACKGROUND: Senescent RBCs bear IgG and C3 opsonins that are three to four times less than required for similar phagocytosis of experimentally opsonized RBCs. STUDY DESIGN AND METHODS: Studies were performed to determine the phagocyte receptors involved in phagocytosis in vitro. The effect of clustering of opsonins and oxidative damage in the sequestration of RBCs was studied by exposing RBCs to BS3 (bis[sulfosuccinimidyl]-suberate) and diamide (azodicarboxylic acid bis[dimethyl-amide]). RESULTS: Sequestration of senescent RBCs was inhibited by the treatment of lymphokine-activated monocytes with N-acetyl-D-galactoseamine (GalNAc), arginine-glycine-aspartic acid (RGD), or antibodies to CR3, FcgammaRI, FcgammaRII, leukocyte response integrin (LRI), and integrin-associated protein (IAP). Exposure to BS3 alone did not enhance phagocytosis. The addition of serum resulted in opsonin binding. The level of opsonization required for sequestration was higher than on senescent RBCs and was only marginally inhibited by blocking CR3, FcgammaRI and FcgammaRII. Diamide treatment alone did not lead to sequestration. Diamide-treated RBCs exposed to serum bound opsonin much as did senescent RBCs, and sequestration was inhibited by GalNAc, RGD, and antibodies to CR3, FcgammaRI, FcgammaRII, LRI, and IAP. CONCLUSION: Membrane alterations resulting in the binding of opsonins and the sequestration of senescent RBCs may be similar to those that occur on diamide-oxidized RBCs. They suggest the need for cooperative events among oxidation, clustering and cross-linking, and serum opsonization.
Complement C3↗
In vivo administration of intravenous immunoglobulin (IVIg) can lead to enhanced erythrocyte sequestration.
Enhanced erythrocyte sequestration is one of the very few major adverse effects of intravenous immunoglobulin (IVIg). IVIg contains high molecular weight IgG complexes ( approximately 300 kDa) which, in the presence of serum, mimic immune complexes by activating complement, binding to CR1 of red blood cells (RBC) (CD35) and mediating erythrophagocytosis. Four of seven patients undergoing IVIg therapy showed significant drops in haematocrit and haemoglobin that were not due to isoantibodies in the IVIg. Prior to treatment, patients' RBC carried IgG and complement (C') 3d that were not bound as immune complexes via CR1 (CD35). The patients whose RBC bound immune complex-like moieties and showed drops in haematocrit and haemoglobin subsequent to IVIg were young adults (22-35 years); older patients (50-69 years) showed no ill effects. In the presence of complement, RBC of young patients bound IVIg complexes in vitro while those of older patients did not. It is not the absolute levels of erythrocyte-associated IgG or C'3 fragments, neither pre- nor post-therapy, which are predictive of IVIg associated decreases in haematocrit and haemoglobin levels. Patient age and RBC inability to bind the IVIg immune complex-like moieties in vitro both appear to be predictors of resistance to sequestration after in vivo treatment with IVIg.
Adult↗
New antifungal agents that inhibit the growth of Candida species: dichlorinated 8-quinolinols.
Five dichlorinated 8-quinolinols (2,5- 5,6-, 3,5-, 3,7-, and 4,5-dichloro-8-quinolinol) were tested against Candida albicans and C. tropicalis in Sabouraud dextrose broth with and without bovine serum. The 5,6-, 3,5-, and 3,7-dichloro-8-quinolinols proved to be more effective than the control, 5-fluorocytosine. In cytotoxicity tests employing baby hamster kidney (BHK) cells, all test agents proved to be more cytotoxic than the control. However, the minimum inhibitory concentration (MIC) of 3,5-dichloro-8-quinolinol to both fungi was only one tenth the cytotoxic dose, suggesting that the compound may be useful as a topical or systemic antifungal agent.
Animals↗
Isoantibodies in immunoglobulin for intravenous use may cause erythrocyte sequestration.
BACKGROUND AND OBJECTIVES: IVIg, while generally a safe therapy for a variety of immunological disorders, can have detrimental effects on erythrocyte (RBC) homeostasis. We studied the mediation of erythrophagocytosis by isoantibodies in IVIg. MATERIALS AND METHODS: RBC were exposed to IVIg and binding of IgG determined by flow cytometry. In vitro phagocytosis of these RBC was assayed. RESULTS: Anti-A and anti-B in IVIg mediate Fc-dependent erythrophagocytosis even in the presence of excess IVIg. Removal of these isoantibodies from IVIg prevents IgG binding and erythrophagocytosis. Complement enhances IVIg-mediated RBC sequestration. CONCLUSION: It may be desirable to remove isoantibodies from IVIg especially for anemic patients or those who respond to the IVIg with a hemolytic episode.
Adolescent↗
Immune complex-like moieties in immunoglobulin for intravenous use (i.v.Ig) bind complement and enhance phagocytosis of human erythrocytes.
Treatment with i.v.Ig can, on rare occasions, lead to detrimental effects such as enhanced erythrocyte sequestration and an increase in serum immune complexes with inflammatory sequellae such as exacerbation of glomerular nephritis. In this study, i.v.Ig (Sandoglobin) was examined for complement binding moieties which resemble immune complexes and can mediate the binding of IgG and C'3b to human erythrocytes via CR1 and enhance erythrocyte susceptibility to sequestration. Sephacryl S-200 HR separated i.v.Ig into two fractions: monomeric IgG (74%) and larger complexes of the molecular weight of an IgG dimer or greater (> or = 300 kD) (26%). In the presence of complement, the 'dimers' bound to human erythrocytes, rendering them susceptible to phagocytosis in vitro. Removal of erythrocyte-specific isoantibodies from the i.v.Ig had no effect on 'dimer' binding to the erythrocytes. Monomeric IgG contained virtually no complement-activating, erythrocyte-binding activity. Erythrocyte binding of complement-bearing IgG 'dimers' and subsequent phagocytosis resembles the binding of complement-bearing immune complexes to erythrocyte CR1. Exposure to Factor I leads to the release of complement-bearing IgG 'dimers' from erythrocyte CR1 and to the abrogation of erythrophagocytosis. Binding of complement-bearing IgG 'dimers' to the erythrocyte is blocked by To5, a CR1-specific monoclonal antibody.
Adolescent↗
Developing a successful product line strategy.
By looking beyond traditional organizational boundaries and integrating the clinical and administrative activities from a system perspective, providers and their partners will improve their ability to compete by providing better, more effective care.
Accounting↗
National survey results. Behavioral integrated systems come of age.
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Delivery of Health Care, Integrated↗
Depression and immunity: the biochemical interrelationship between the central nervous system and the immune system.
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Adult↗
Cloning of a urochordate cDNA featuring mammalian short consensus repeats (SCR) of complement-control protein superfamily.
Mammalian tumor necrosis factor (TNF)-alpha degenerate polymerase chain reaction (PCR) primers were used to amplify a probe from Botryllus schlosseri (colonial ascidian) allogeneic rejection-cDNA library. A PCR product (269 bp) was cloned and sequenced encoding an open reading frame (ORF) of 89 amino acids (aa). This clone, which revealed no similarity to TNF-alpha, but a substantial similarity to mammalian proteins featuring short consensus repeats (SCRs) of the complement control superfamily, was used to probe the rejection-cDNA library. Two partial cDNA clones were isolated and sequenced (Bs.1, 846 bp; Bs.2, 712 bp). The longest ORF in clone Bs.1 (which lacks the 5' end of the cDNA) predicts a protein of 251 aa, which differs from Bs.2 at six nucleotides and four aa. We compare the aa similarity (up to 50.5%) of Bs.1 with the SCR-region of mammalian complement factor H, apolipoprotein H, selectins, and complement receptors type 1 and type 2. A somatomedin B-like domain at the C-terminus of Bs.1 deduced protein was also recorded. We propose that this mosaic and polymorphic botryllid sequence, featuring mammalian-like SCRs, might be an ancestral molecule in the evolution of the chordate's complement-control protein superfamily.
Amino Acid Sequence↗
Direct typing of polymorphic microsatellites in the colonial tunicate Botryllus schlosseri (ASCIDIACEA).
Five microsatellite loci of the marine protochordate Botryllus schlosseri were cloned: four of uninterrupted (AG)n repeats and one of both (AG)n and (TG)n repeats. By means of an innovative procedure small colony fragments were minimally treated to serve as templates for PCR with microsatellite-specific primers. Four of the loci were polymorphic: 7-8 discrete alleles were scored in nine colonies, heterozygosity ranging between 44-80%. At locus number 811 spacing of the alleles and gel-resolution were highest, therefore, ten additional colonies were typed and in total nine alleles were scored with maximal allelic interval of 120 base pair and 53% heterozygous colonies. The high levels of microsatellite-polymorphism provide a new tool as individual markers for studies on aspects of the botryllid polymorphic allorecognition system.
Animals↗
Erythrocytes from young but not elderly donors can bind and degrade immune complex- and antibody-bound C3 in vitro.
In situ aged erythrocytes (senescent erythrocytes from young donors and both young and old erythrocytes from elderly donors) demonstrate high levels of membrane-bound C3c and C3d and elevated susceptibility to in vitro phagocytosis. In this study we demonstrate that in situ aged erythrocytes are defective in their ability to degrade C3 fragments and clear them from the erythrocyte membrane. Erythrocytes from young donors bind complement-bearing immune complexes via CR1 and become susceptible to complement-mediated erythrophagocytosis ('innocent bystander' sequestration). Erythrocytes from elderly donors are defective in their ability to bind such immune complexes, as attested by the lack of an increment in membrane-associated C3 fragments as detected by flow cytometry and lack of an increment in in vitro sequestration. Factor I (serum)-dependent cleavage of C3 fragments and release of immune complexes from the erythrocytes of young donors lead to a drop in erythrocyte-associated C3 fragments and the disappearance of the 'innocent bystander' phenomenon. Inhibition of Factor I, and thus inhibition of C3b degradation and immune complex release for the erythrocyte membrane, enhances the levels of 'innocent bystander' sequestration of erythrocytes from young donors. Erythrocytes from elderly donors are defective in the dynamic process of CR1 binding of complement-bearing immune complexes and Factor I-associated release of membrane-associated C3 fragments. A defect in the ability of all in situ aged erythrocytes to clear their membranes of C3 fragments is also demonstrated for complement bound to the erythrocyte via IgM isoagglutinins. While erythrocytes from both young and elderly donors allow for the IgM-mediated binding of complement to the erythrocyte, only young erythrocytes from young donors demonstrate degradative activity with the release of membrane-associated C3c. Erythrocytes from elderly donors demonstrate lower levels of detectable CR1 (CD35), decay accelerating factor (DAF) (CD55) and Protectin (CD59) than do erythrocytes from young donors. Time course studies determine that the defect in handling of immune complexes observed for in situ aged erythrocytes is not due to differences in the kinetics of loading or releasing of immune complexes. These findings on the refractiveness of erythrocytes of elderly donors to uptake of immune complexes and the degradation of C3 fragments may be of importance not only in the understanding of erythrocyte sequestration, but also in the physiology of immune clearance in the elderly.
Adolescent↗
cDNA cloning of a putative protochordate FK506-binding protein.
A tunicate (Botryllus schlossert) cDNA library was screened with a microsatellite probe. Five positive clones were sequenced, each with a 5' truncated microsatellite. One (Bs.6) revealed striking similarity to FK506 and rapamycin-binding proteins (FKBPs). Clone Bs.6 is 500 base pairs long and encodes for a putative protein of 134 amino acids. The predicted protein features the two FKBP-type peptidyl-prolyl cis-trans isomerase (PPIase) signatures and an endoplasmic reticulum retention signal. This protochordate protein is substantially similar to 12-13 kDa FKBPs, most remarkably to one of the receptors that had been proposed to mediate the immunosuppressive actions of FK506, the human FKBP-13 (62% amino acid identity and 74% similarity).
Amino Acid Sequence↗
Mode of formation and structural features of DNA-cationic liposome complexes used for transfection.
Complexes formed between cationic liposomes and nucleic acids represent a highly efficient vehicle for delivery of DNA and RNA molecules into a large variety of eukaryotic cells. By using fluorescence, gel electrophoresis, and metal-shadowing electron microscopy techniques, the factors that affect the, yet unclear, interactions between DNA and cationic liposomes as well as the structural features of the resulting complexes have been elucidated. A model is suggested according to which cationic liposomes bind initially to DNA molecules to form clusters of aggregated vesicles along the nucleic acids. At a critical liposome density, two processes occur, namely, DNA-induced membrane fusion, indicated by lipid mixing studies, and liposome-induced DNA collapse, pointed out by the marked cooperativity of the encapsulation processes, by their modulations by DNA-condensing agents, and also by their conspicuous independence upon DNA length. The DNA collapse leads to the formation of condensed structures which can be completely encapsulated within the fused lipid bilayers in a fast, highly cooperative process since their exposed surface is substantially smaller than that of extended DNA molecules. The formation of the transfecting DNA-liposome complexes in which the nucleic acids are fully encapsulated within a positively-charged lipid bilayer is proposed, consequently, to be dominated by mutual effects exerted by the DNA and the cationic liposomes, leading to interrelated lipid fusion and DNA collapse.
Animals↗
A role for complement as the major opsonin in the sequestration of erythrocytes from elderly and young donors.
Erythrocytes from elderly donors (> 70 years), but not young donors (18-35 years), are shown to undergo sequestration in an in vitro erythrophagocytosis assay. Comparable levels of sequestration are observed for high density erythrocytes from young individuals and both low density and high density erythrocytes from elderly individuals. These cells, which are susceptible to phagocytosis with no additional treatment are collectively termed 'in situ aged' erythrocytes. We present evidence for the involvement of complement in the sequestration of 'in situ aged' erythrocytes and correlate levels of complement bound to 'in situ aged' erythrocytes from young and elderly donors with levels of phagocytosis. We also demonstrate that the in vitro sequestration of erythrocytes from elderly donors can be inhibited by beta-galactosyl sugars and arginine-glycine-aspartic acid (RGD) but not by mannose nor by Protein-G, a specific inhibitor of Fc-gamma mediated phagocytosis. These experiments show that IgG is not the major opsonin in the sequestration of red cells from elderly donors. In support of the role of complement rather than IgG as the major opsonin in red cell sequestration, we further demonstrate that C'3 bearing immune complexes block in vitro sequestration of erythrocytes from elderly donors. This competition is not dependent upon the isotype of the immunoglobulin (IgM or IgG) in the complex but rather on the presence of active complement.
Adolescent↗
Exposure to complement-bearing immune complexes enhances the in vitro sequestration of erythrocytes from young but not elderly donors.
Complement and immunoglobulin have each been claimed to be the major opsonins responsible for sequestration of the effete erythrocyte. Binding of immune complexes to the erythrocyte via CR1 (CD35) provides a model for studying the effects of increments in membrane-bound complement and immunoglobulin on the sequestration of the erythrocyte ('innocent bystander' sequestration). It is possible that C3b-bearing immune complexes (IC-C3b) bound to erythrocyte CR1 contribute to the levels of immunoglobulin and complement fragments detectable on the human erythrocyte. We have, therefore, compared the capacity of erythrocytes from young and elderly donors to bind IC-C3b and the effect of this binding on in vitro sequestration. Erythrocytes from young donors exposed to IC-C3b bind these complexes, as attested by an increment in membrane-bound C3, and undergo 'innocent bystander' sequestration. However, when density-separated erythrocytes are so exposed, it is only the low density (young) erythrocytes from young donors which are susceptible to 'innocent bystander' sequestration. High density (old) erythrocytes from young donors and all erythrocytes from elderly donors show initially high in vitro sequestration and are resistant to the 'innocent bystander' effect. (Those erythrocytes which show initially high in vitro sequestration are referred to collectively as 'in situ aged' erythrocytes.) There is a great similarity between the mechanisms of sequestration of 'in situ aged' and 'innocent bystander' erythrocytes in that they are both inhibited by the integrin binding peptide arginine-glycine-aspartic acid (RGD) and the beta-galactosyl sugar N-acetyl-galactosamine, and unaffected by the Fc-gamma binding protein, Protein-G. Complement is the major opsonin in 'innocent bystander' sequestration since this sequestration occurs whether the isotype of the antibody in the immune complex is IgM or IgG, and Protein-G, which inhibits IgG-dependent erythrophagocytosis, has no effect on 'innocent bystander' sequestration. The present studies demonstrate that in vitro sequestration of 'in situ aged' erythrocytes is similar to complement-dependent 'innocent bystander' sequestration, thus supporting the contention that complement recognition is cardinal in sequestration of 'in situ aged' erythrocytes.
Adolescent↗