Adhesion and signaling in vascular cell--cell interactions.
Muscle wasting in insulinopenic rats results from activation of the ATP-dependent, ubiquitin-proteasome proteolytic pathway by a mechanism including gene transcription.
S R Price, J L Bailey, X Wang, C Jurkovitz, B K England, X Ding, L S Phillips, W E MitchAbstract | Full text | PDF (Page 1703)
In normal subjects and diabetic patients, insulin suppresses whole body proteolysis suggesting that the loss of lean body mass and muscle wasting in insulinopenia is related to increased muscle protein degradation. To document how insulinopenia affects organ weights and to identify the pathway for accelerated proteolysis in muscle, streptozotocin-treated and vehicle-injected, pair-fed control rats were studied. The weights of liver, adipose tissue, and muscle were decreased while muscle protein degradation was increased 75% by insulinopenia. This proteolytic response was not eliminated by blocking lysosomal function and calcium-dependent proteases at 7 or 3 d after streptozotocin. When ATP synthesis in muscle was inhibited, the rates of proteolysis were reduced to the same level in insulinopenic and control rats suggesting that the ATP-dependent, ubiquitin-proteasome pathway is activated. Additional evidence for activation of this pathway in muscle includes: (a) an inhibitor of proteasome activity eliminated the increased protein degradation; (b) mRNAs encoding ubiquitin and proteasome subunits were increased two- to threefold; and (c) there was increased transcription of the ubiquitin gene. We conclude that the mechanism for muscle protein wasting in insulinopenia includes activation of the ubiquitin-proteasome pathway with increased expression of the ubiquitin gene.
Autoimmunity in Chagas' disease. Identification of cardiac myosin-B13 Trypanosoma cruzi protein crossreactive T cell clones in heart lesions of a chronic Chagas' cardiomyopathy patient.
E Cunha-Neto, V Coelho, L Guilherme, A Fiorelli, N Stolf, J KalilAbstract | Full text | PDF (Page 1709)
Heart tissue destruction in chronic Chagas' disease cardiomyopathy (CCC) may be caused by autoimmune recognition of heart tissue by a mononuclear cell infiltrate decades after Trypanosoma cruzi infection. Indirect evidence suggests there is molecular mimicry between T. cruzi and heart tissue. In murine models of CCC, antibodies and CD4+ T cells recognize myosin, the major heart protein. We recently identified a heart-specific epitope of cardiac myosin heavy chain (residues 1442-1447, AAALDK) that is crossreactive with a homologous sequence (AAAGDK) of the immunodominant T. cruzi antigen B13. Furthermore, cardiac myosin-B13 crossreactive antibodies are present in 100% CCC patients vs 14% asymptomatic T. cruzi-seropositive individuals (P = 2.3 x 10(-6)), suggesting a role for molecular mimicry between cardiac myosin and B13 in CCC pathogenesis. In this paper, we obtained heart-infiltrating T cell clones from CCC patients to assess whether molecular mimicry between cardiac myosin and B13 is directly involved in the genesis of heart lesions. We identified T cell clones derived from CCC heart lesions simultaneously responsive to cardiac myosin heavy chain (but not skeletal myosin heavy chain) and B13 T. cruzi protein, but could not find T cell clones primarily reactive to any T. cruzi antigen. Together with the association of myosin-B13 crossreactive antibodies with CCC, the present data strongly suggest the relevance of molecular mimicry between cardiac myosin and the T. cruzi protein B13 in the pathogenesis of heart lesions in chronic Chagas' disease cardiomyopathy.
Acute lung injury fibroblast migration and invasion of a fibrin matrix is mediated by CD44.
K Svee, J White, P Vaillant, J Jessurun, U Roongta, M Krumwiede, D Johnson, C HenkeAbstract | Full text | PDF (Page 1713)
Fibrosis results when myofibroblasts invade the wound fibrin provisional matrix. Extracellular matrix receptors on the cell surface mediate cell adhesion, migration, and invasion. Recent work with transformed cells indicates that these cells use the cell surface matrix receptor CD44 for migration and invasion. In this study, we examine whether lung fibroblasts, isolated from patients dying with acute alveolar fibrosis, use CD44 to invade a fibrin matrix. Consistent with a role for CD44 in mediating fibroblast invasion and subsequent tissue fibrosis, immunohistochemical analysis of lung tissue from patients who died from acute alveolar fibrosis after lung injury reveals CD44-expressing mesenchymal cells throughout newly formed fibrotic tissue. PCR, Western, and immunoprecipitation analysis demonstrate that the 85-kD CD44 isoform is expressed by acute lung injury fibroblasts. Consistent with a role in mediating matrix adhesion and migration ultrastructurally, CD44 was found uniformly over the cell surface and was found densely labeling filopodia and lamellipodia, highly motile structures involved in cell migration. To determine if lung injury fibroblasts use CD44 to invade fibrin, a fibrin gel model of fibrosis was used. By blocking the function of CD44 with monoclonal antibodies, fibroblast invasion into a fibrin matrix was inhibited. To examine the mechanism by which CD44 mediates fibroblast invasion, the role of CD44 in fibroblast migration and adhesion was evaluated. Anti-CD44 antibody blocked fibroblast migration on the provisional matrix proteins fibronectin, fibrinogen, and hyaluronic acid. Additionally, fibroblast CD44 mediated adhesion to the provisional matrix proteins fibronectin, fibrin, and hyaluronic acid, but not to laminin, a component of the basement membrane. These findings support the hypothesis that fibroblast CD44 functions as an adhesion receptor for provisional matrix proteins and is capable of mediating fibroblast migration and invasion of the wound provisional matrix resulting in the formation of fibrotic tissue.
G-protein alpha subunit Gi(alpha)2 mediates erythropoietin signal transduction in human erythroid precursors.
B A Miller, L Bell, C A Hansen, J D Robishaw, M E Linder, J Y CheungAbstract | Full text | PDF (Page 1728)
Erythropoietin induces a dose-dependent increase in cytosolic calcium in human erythroblasts that is mediated by a voltage-independent Ca2+ channel. Inhibition of this response to erythropoietin by pertussis toxin suggests involvement of guanine nucleotide-binding regulatory proteins (G-proteins). The role of G-proteins in regulation of the erythropoietin-modulated Ca2+ channel was delineated here by microinjection of G-protein modulators or subunits into human erythroid precursors. This is the first report on the use of microinjection to study erythropoietin signal transduction in normal precursor cells. Fura-2 loaded day-10 burst-forming units-erythroid-derived erythroblasts were used for microinjection and free intracellular calcium concentration ([Ca(i)]) was measured with digital video imaging. BCECF (1,2',7'-bis(2-carboxyethyl)-5-(and -6-)-carboxyfluorescein) was included in microinjectate, and an increase in BCECF fluorescence was evidence of successful microinjection. Cells were microinjected with nonhydrolyzable analogues of GTP, GTPgammaS or GDPbetaS, which maintain the alpha subunit in an activated or inactivated state, respectively. [Ca(i)] increased significantly in a dose-dependent manner after microinjection of GTPgammaS. However, injection of GDPbetaS blocked the erythropoietin-induced calcium increase, providing direct evidence that activation of a G-protein is required. To delineate which G-protein subunits are involved, alpha or betagamma transducin subunits were purified and microinjected as a sink for betagamma or alpha subunits in the erythroblast, respectively. Transducin betagamma, but not alpha, subunits eliminated the calcium response to erythropoietin, demonstrating the primary role of the alpha subunit. Microinjected antibodies to Gi(alpha)2, but not Gi(alpha)1 or Gi(alpha)3, blocked the erythropoietin-stimulated [Ca(i)] rise, identifying Gi(alpha)2 as the subunit involved. This was confirmed by the ability of microinjected recombinant myristoylated Gi(alpha)2, but not Gi(alpha)1 or Gi(alpha)3 subunits, to reconstitute the response of pertussis toxin-treated erythroblasts to erythropoietin. These data directly demonstrate a physiologic function of G-proteins in hematopoietic cells and show that Gi(alpha)2 is required in erythropoietin modulation of [Ca(i)] via influx through calcium channels.
Triiodothyronine induces over-expression of alpha-smooth muscle actin, restricts myofibrillar expansion and is permissive for the action of basic fibroblast growth factor and insulin-like growth factor I in adult rat cardiomyocytes.
M A Gosteli-Peter, B A Harder, H M Eppenberger, J Zapf, M C SchaubAbstract | Full text | PDF (Page 1737)
Effects of triiodothyronine (T3) on the expression of cytoskeletal and myofibrillar proteins in adult rat cardiomyocytes (ARC) were followed during two weeks of culture in the presence of 20% T3-depleted (stripped) FCS. Control cultures expressed mainly beta-myosin heavy chain (MHC) mRNA. T3 caused a switch to alpha-MHC expression and a dose-dependent increase of alpha-smooth muscle (alpha-sm) actin mRNA and protein. In parallel, the number of alpha-sm actin immunoreactive cells increased from 1% in controls to 29 and 62% in ARC treated with 5 and 100 nM T3. In the presence of T3, cells exhibited a higher beating rate than controls. The distribution of myofibrils in T3-treated cells was restricted to the perinuclear area with a sharp boundary. Only 5% of the control cells but 30 and 62% of the T3-treated (5 and 100 nM) ARC showed this restricted myofibrillar phenotype. Basic fibroblast growth factor (bFGF) which restricts myofibrillar growth and upregulates alpha-sm actin in ARC cultured with normal FCS had no effect on alpha-sm actin in ARC cultured in stripped FCS, but potentiated the effect of T3. In contrast, insulin-like growth factor I (IGF I), which suppresses alpha-sm actin and stimulates myofibrillogenesis in the presence of normal FCS suppressed T3-induced alpha-sm actin expression in stripped FCS. Thus, T3 appears to be permissive for the action of bFGF and IGF I on alpha-sm actin expression.
Glanzmann thrombasthenia. Cooperation between sequence variants in cis during splice site selection.
Y Jin, H C Dietz, R A Montgomery, W R Bell, I McIntosh, B Coller, P F BrayAbstract | Full text | PDF (Page 1745)
Glanzmann thrombasthenia (GT), an autosomal recessive bleeding disorder, results from abnormalities in the platelet fibrinogen receptor, GP(IIb)-IIIa (integrin alpha(IIb)beta3). A patient with GT was identified as homozygous for a G-->A mutation 6 bp upstream of the GP(IIIa) exon 9 splice donor site. Patient platelet GP(IIIa) transcripts lacked exon 9 despite normal DNA sequence in all of the cis-acting sequences known to regulate splice site selection. In vitro analysis of transcripts generated from mini-gene constructs demonstrated that exon skipping occurred only when the G-->A mutation was cis to a polymorphism 116 bp upstream, providing precedence that two sequence variations in the same exon which do not alter consensus splice sites and do not generate missense or nonsense mutations, can affect splice site selection. The mutant transcript resulted from utilization of a cryptic splice acceptor site and returned the open reading frame. These data support the hypothesis that pre-mRNA secondary structure and allelic sequence variants can influence splicing and provide new insight into the regulated control of RNA processing. In addition, haplotype analysis suggested that the patient has two identical copies of chromosome 17. Markers studied on three other chromosomes suggested this finding was not due to consanguinity. The restricted phenotype in this patient may provide information regarding the expression of potentially imprinted genes on chromosome 17.
Impaired hepatic glycogen synthesis in glucokinase-deficient (MODY-2) subjects.
G Velho, K F Petersen, G Perseghin, J H Hwang, D L Rothman, M E Pueyo, G W Cline, P Froguel, G I ShulmanAbstract | Full text | PDF (Page 1755)
All glucokinase gene mutations identified to date have been localized to exons that are common to the pancreatic and hepatic isoforms of the enzyme. While impaired insulin secretion has been observed in glucokinase-deficient subjects the consequences of this mutation on hepatic glucose metabolism remain unknown. To examine this question hepatic glycogen concentration was measured in seven glucokinase-deficient subjects with normal glycosylated hemoglobin and 12 control subjects using 13C nuclear magnetic spectroscopy during a day in which three isocaloric mixed meals were ingested. The relative fluxes of the direct and indirect pathways of hepatic glycogen synthesis were also assessed using [1-13C]glucose in combination with acetaminophen to noninvasively sample the hepatic UDP-glucose pool. Average fasting hepatic glycogen content was similar in glucokinase-deficient and control subjects (279+/-20 vs 284+/-14 mM; mean+/-SEM), and increased in both groups after the meals with a continuous pattern throughout the day. However, the net increment in hepatic glycogen content after each meal was 30-60% lower in glucokinase-deficient than in the control subjects (breakfast, 46% lower, P < 0.02; lunch, 62% lower, P = 0.002; dinner; 30% lower, P = 0.04). The net increment over basal values 4 h after dinner was 105 +/-18 mM in glucokinase-deficient and 148+/-11 mM in control subjects (P = 0.04). In the 4 h after breakfast, flux through the gluconeogenic pathway relative to the direct pathway of hepatic glycogen synthesis was higher in glucokinase-deficient than in control subjects (50+/-2% vs 34+/-5%; P = 0.038). In conclusion glucokinase-deficient subjects have decreased net accumulation of hepatic glycogen and relatively augmented hepatic gluconeogenesis after meals. These results suggest that in addition to the altered beta cell function, abnormalities in liver glycogen metabolism play an important role in the pathogenesis of hyperglycemia in patients with glucokinase-deficient maturity onset diabetes of young.
Genetic linkage of IgG autoantibody production in relation to lupus nephritis in New Zealand hybrid mice.
F1 hybrids of New Zealand black (NZB) and New Zealand white (NZW) mice are a model of human systemic lupus erythematosus. These mice develop a severe immune com-plex-mediated nephritis, in which antinuclear autoantibodies are believed to play the major role. We used a genetic analysis of (NZB x NZW)F1 x NZW backcross mice to provide insight into whether different autoantibodies are subject to separate genetic influences and to determine which autoantibodies are most important in the development of lupus-like nephritis. The results showed one set of loci that coordinately regulated serum levels of IgG antibodies to double-stranded DNA, single-stranded DNA, total histones, and chromatin, which overlapped with loci that were linked to the production of autoantibodies to the viral glycoprotein, gp70. Loci linked with anti-gp70 compared with antinuclear antibodies demonstrated the strongest linkage with renal disease, suggesting that autoantibodies to gp70 are the major pathogenic antibodies in this model of lupus nephritis. Interestingly, a distal chromosome 4 locus, Nba1, was linked with nephritis but not with any of the autoantibodies measured, suggesting that it contributes to renal disease at a checkpoint distal to autoantibody production.
Direct preconditioning of cultured chick ventricular myocytes. Novel functions of cardiac adenosine A2a and A3 receptors.
Preconditioning with brief ischemia before a sustained period of ischemia reduces infarct size in the perfused heart. A cultured chick ventricular myocyte model was developed to investigate the role of adenosine receptor subtypes in cardiac preconditioning. Brief hypoxic exposure, termed preconditioning hypoxia, prior to prolonged hypoxia, protected myocytes against injury induced by the prolonged hypoxia. Activation of the adenosine A1 receptor with CCPA or the A3 receptor with C1-IB-MECA can replace preconditioning hypoxia and simulate preconditioning, with a maximal effect at 100 nM. While activation of the A2a receptor by 1 microM CGS21680 could not mimic preconditioning, its stimulation during preconditioning hypoxia, however, attenuated the protection against hypoxia-induced injury. Blockade of A2a receptors with the selective antagonist CSC (1 microM) during preconditioning hypoxia enhanced the protective effect of preconditioning. Nifedipine, which blocked the A2a receptor-mediated calcium entry, abolished the A2a agonist-induced attenuation of preconditioning. Isoproterenol, forskolin, and BayK 8644, which stimulated calcium entry, also attenuated preconditioning. Nifedipine blocked the increase in calcium uptake by these agents as well as their attenuating effect on preconditioning. The present study provides the first evidence that the adenosine A3 receptor is present on ventricular myocytes and can mediate simulation of preconditioning. The data demonstrate, for the first time, that activation of the A2a receptor antagonizes the preconditioning effect of adenosine, with increased calcium entry during the preconditioning stimuli as a novel mechanism.
Mechanisms of impaired beta-adrenoceptor-induced airway relaxation by interleukin-1beta in vivo in the rat.
H Koto, J C Mak, E B Haddad, W B Xu, M Salmon, P J Barnes, K F ChungAbstract | Full text | PDF (Page 1780)
We studied the in vivo mechanism of beta-adrenergic receptor (beta-AR) hyporesponsiveness induced by intratracheal instillation of interleukin-1beta (IL-1beta, 500 U) in Brown-Norway rats. Tracheal and bronchial smooth muscle responses were measured under isometric conditions ex vivo. Contractile responses to electrical field stimulation and to carbachol were not altered, but maximal relaxation induced by isoproterenol (10(-6)-10(-5) M) was significantly reduced 24 h after IL-1beta treatment in tracheal tissues and to a lesser extent, in the main bronchi. Radioligand binding using [125I]iodocyanopindolol revealed a 32+/-7% reduction in beta-ARs in lung tissues from IL-1beta-treated rats, without any significant changes in beta2-AR mRNA level measured by Northern blot analysis. Autoradiographic studies also showed significant reduction in beta2-AR in the airways. Isoproterenol-stimulated cyclic AMP accumulation was reduced by IL-1beta at 24 h in trachea and lung tissues. Pertussis toxin reversed this hyporesponsiveness to isoproterenol but not to forskolin in lung tissues. Western blot analysis revealed an IL-1beta-induced increase in Gi(alpha) protein expression. Thus, IL-1beta induces an attenuation of beta-AR-induced airway relaxation through mechanisms involving a reduction in beta-ARs, an increase in Gi(alpha) subunit, and a defect in adenylyl cyclase activity.
Requirement for increased IL-10 in the development of B-1 lymphoproliferative disease in a murine model of CLL.
S Ramachandra, R A Metcalf, T Fredrickson, G E Marti, E RavecheAbstract | Full text | PDF (Page 1788)
Malignant B-1 cells derived from NZB mice, a murine model of spontaneous autoimmunity and B cell lymphoproliferative disease, produce significantly higher levels of IL-10 mRNA than normal B-1 or B cells. IL-10 may act as an autocrine growth factor for the expansion of malignant B-1 cells. In order to determine if elevated endogenous production of IL-10 was a required element for the malignant transformation of B-1 cells in NZB mice, backcross animals were studied for the linkage between elevated IL-10 expression and the presence of lymphoid malignancy. The phenotypes of aged (NZB x DBA/2)F1 x NZB animals were determined and a strong correlation was found between the elevated levels of IL-10 mRNA and the development of B-1 malignant clones. In contrast, an increased level of IL-10 message was not associated with elevated serum IgM or the presence of anemia or reticulocytosis which is mainly seen in response to autoantibody production. These results indicate that, at least in NZB, the autoimmunity and lymphoproliferation phenotypes are not linked genetically. IL-10 may enhance proliferation and the development of B-1 cell malignancy rather than antibody production by the B-1 cell subpopulation. Thus, IL-10 plays an important role in B-1 malignancies, and downregulation of IL-10 could be a likely site for intervention in B cell malignancies.
Human immunodeficiency virus-1 (HIV-1) gp120 superantigen-binding serum antibodies. A host factor in homosexual HIV-1 transmission.
J Townsley-Fuchs, L Kam, R Fairhurst, S J Gange, L Goodglick, J V Giorgi, N Sidell, R Detels, J BraunAbstract | Full text | PDF (Page 1794)
HIV-1 gp120 is an immunoglobulin superantigen which can bind to preimmune serum Ig. We hypothesize that levels of such preimmune antibodies vary in the population and might affect host resistance or susceptibility to viral transmission. This study tests two predictions: (a) levels of preimmune anti-gpl20 Igs are a polymorphic trait; and, (b) these levels are correlated with resistance or susceptibility to HIV-1 transmission. The first prediction was confirmed in a longitudinal study of a low-risk seronegative population. In this group, levels of both endogenous anti-gpl20 IgM and IgG varied widely, but were characteristic and stable for each individual. The second prediction was addressed in a study of participants of the Multicenter AIDS Cohort Study, in which men "susceptible" and "resistant" to HIV infection were identified based on numbers of sexual partners and eventual seroconversion. Specimens consisted of archival sera obtained > 2 yr before seroconversion. Men in the susceptible population (low-risk seroconverters) were distinguished by low levels of anti-gpl20 IgG. We conclude that the level of preimmune anti-gpl20 IgG is a polymorphic population trait, and low levels are a potentially specific and significant factor in homosexual transmission of HIV infection.
Molecular identification of T cells that respond in a primary bulk culture to a peptide derived from a platelet glycoprotein implicated in neonatal alloimmune thrombocytopenia.
Neonatal alloimmune thrombocytopenia induced by the human platelet alloantigen 1a (HPA1a) is characterized by generation of alloantibodies by a mother who is homozygous for the HPA1b alloantigen and almost always HLA-DRB3*0101. The disease is viewed as B cell mediated but the linkage with HLA is indicative of a role for T cells. The HPA1a and HPA1b allotypes are defined, respectively, by Leu and Pro at amino acid 33 of the beta-chain of the platelet integrin GPIIbIIIa (alpha(IIb)beta3). Under the assumption that the same polymorphism may control both the B cell epitope and constitute the MHC-bound peptide, we restimulated PBMC from a woman with an affected child with a synthetic peptide from this polymorphic region. Molecular analysis of the responding T cell repertoire identified two T cells which predominated in cultures stimulated with the alloantigen peptide and which were absent in cultures with the autoantigen peptide. In spite of the use of different V families, sequence of the CDR3 region of the T cell receptor (TCR) beta-chain revealed the presence of a shared motif, L-P-S/T. Oligonucleotide probes specific for the CDR3 sequence indicated that these T cells were present in the PBMC at the highest levels immediately after delivery of the affected infant and their frequency dropped at later times.
A carboxy-terminal truncation of human alpha-galactosidase A in a heterozygous female with Fabry disease and modification of the enzymatic activity by the carboxy-terminal domain. Increased, reduced, or absent enzyme activity depending on number of amino acid residues deleted.
N Miyamura, E Araki, K Matsuda, R Yoshimura, N Furukawa, K Tsuruzoe, T Shirotani, H Kishikawa, K Yamaguchi, M ShichiriAbstract | Full text | PDF (Page 1809)
Fabry disease is an X-linked disorder of glycosphingolipid metabolism caused by a deficiency of alpha-galactosidase A (alpha-Gal A). We identified a novel mutation of alpha-Gal A gene in a family with Fabry disease, which converted a tyrosine at codon 365 to a stop and resulted in a truncation of the carboxy (C) terminus by 65 amino acid (AA) residues. In a heterozygote of this family, although the mutant and normal alleles were equally transcribed in cultured fibroblasts, lymphocyte alpha-Gal A activity was approximately 30% of the normal control and severe clinical symptoms were apparent. COS-1 cells transfected with this mutant cDNA showed a complete loss of its enzymatic activity. Furthermore, those cotransfected with mutant and wildtype cDNAs showed a lower alpha-Gal A activity than those with wild type alone (approximately 30% of wild type alone), which suggested the dominant negative effect of this mutation and implied the importance of the C terminus for its activity. Thus, we generated mutant cDNAs with various deletion of the C terminus, and analyzed. Unexpectedly, alpha-Gal A activity was enhanced by up to sixfold compared with wild-type when from 2 to 10 AA residues were deleted. In contrast, deletion of 12 or more AA acid residues resulted in a complete loss of enzyme activity. Our data suggest that the C-terminal region of alpha-Gal A plays an important role in the regulation of its enzyme activity.
Impaired glucose homeostasis in insulin-like growth factor binding protein-1 transgenic mice.
Transgenic mice that overexpressed IGFBP-1 are hyperinsulinemic in the first week of life and gradually develop fasting hyperglycemia. In adult transgenic mice, the hypoglycemic response to IGF-I but not insulin or des (1-3) IGF-I was attenuated (P < 0.05) compared with wild-type mice. Furthermore, in isolated adipocytes from transgenic mice, the stimulatory effect of IGF-I but not insulin on 2-deoxy-[3H]-glucose uptake was reduced (P < 0.02). In contrast, in isolated soleus muscle, the effects of both IGF-I and insulin on 2-deoxy-3H-glucose uptake and on [3H]-glucose incorporation into glycogen were significantly reduced compared to wild-type mice. The decline in specific activity of the 2-deoxy-3H-glucose, a measure of glucose appearance in the circulation, was more marked in transgenic animals (P < 0.05). In addition, tissue uptake of glucose was significantly higher in diaphragm, heart, intestine, liver, soleus muscle, and adipose tissue from fasting transgenic mice. Plasma concentrations of alanine, lysine, and methionine were also elevated in transgenic mice. These data suggest that overexpression of IGFBP-1 attenuates the hypoglycemic effect of endogenous IGF-I, which is initially compensated for by enhanced pancreatic insulin production. However, in adult mice pancreatic insulin content is reduced, insulin resistance is demonstrable in skeletal muscle and fasting hyperglycemia develops.
Insulin and insulin-like growth factor I differentially induce alpha1-adrenergic receptor subtype expression in rat vascular smooth muscle cells.
Hyperinsulinemia has been implicated as an important risk factor for the development of accelerated cardiovascular disease. We wondered if insulin or IGF-I induced expression of alpha1 adrenergic receptors in vascular smooth muscle cells (VSMCs) which could enhance smooth muscle contraction and cell growth activated by catecholamines. Rat aortic VSMCs were incubated with insulin or IGF-I for various times and expression of alpha1 receptors was detected using [3H]prazosin binding. Both insulin and IGF-I increased alpha1 receptor number; also, these peptides increased expression of the alpha1D receptor gene with no change in expression of the alpha1B receptor gene as detected by RNase protection assays. Using Western blotting, we found that these peptides increased expression of the alpha1D receptor subtype in these cells. Increased expression of the alpha1D receptor mRNA was inhibited by the receptor tyrosine kinase inhibitor genistein and the PI 3-kinase inhibitor wortmannin but was not inhibited by protein kinase C inhibitor H7 or the L-type calcium channel blocker nifedipine. Preincubation of cells with insulin or IGF-I enhanced subsequent norepinephrine stimulation of mitogen activated kinase activity. These results suggest that insulin/IGF-I regulate expression of alpha1 receptors in VSMCs and potentially enhance the effects of catecholamines in settings of hyperinsulinemia.
Demonstration of an osteoblast defect in two cases of human malignant osteopetrosis. Correction of the phenotype after bone marrow transplant.
Osteopetrosis is an inherited disorder characterized by bone sclerosis due to reduced bone resorption. Here we report that human osteopetrotic osteoblast-like (Ob) cells express a defective phenotype in primary cultures in vitro, and that bone marrow transplant (BMT) corrects osteoblast function. DNA analysis at polymorphic short-tandem repeat loci from donor, recipient, and primary Ob-like cells pre-BMT and 2 yr post-BMT revealed that Ob were still of recipient origin post-BMT. Osteopetrotic Ob-like cells obtained pre-BMT showed normal and abnormal 1,25(OH)2D3-induced alkaline phosphatase (ALPase) and osteocalcin production, respectively, and failed to produce macrophage colony-stimulating factor (M-CSF) in response to IL-1a and TNF-alpha. These parameters were all normalized in primary Ob-like cells prepared 2 yr post-BMT. X-linked clonality analysis at the human androgen receptor (HUMARA) locus revealed that osteoblasts showed a polyclonal and an oligoclonal derivation pre- and post-BMT respectively, indicating that a limited number of progenitor reconstituted this population. Because osteoblasts were still of recipient origin post-BMT, this suggests that functional osteoclasts, due to the replacement of hematopoeitic cells, provided a local microenvironment in vivo triggering the differentiation and/or recruitment of a limited number of functional osteoblasts.
Characterization of a germline Vk gene encoding cationic anti-DNA antibody and role of receptor editing for development of the autoantibody in patients with systemic lupus erythematosus.
We found previously that cationic anti-DNA autoantibodies (autoAbs) have nephritogenic potential and usage of a specific germline Vk gene, A30, has major influences on cationic charge of the autoAb in human lupus nephritis. In the present study, we have characterized A30 germline Vk gene using cosmid cloning technique in patients with SLE. A30 gene locus locates in less than 250 kb from the Ck region, and the cationic anti-DNA mRNA used the upstream Jk2 gene, indicating that cationic anti-DNA mRNA is a product of primary gene rearrangement. By using PCR technique, we found that A30 gene locus in the genome was defective in eight out of nine SLE patients without nephritis. In contrast, all nine patients with lupus nephritis had intact A30 gene. The presence and absence of A30 gene was associated with the development of lupus nephritis or not (P < 0.01, by Fisher's exact test, two-sided). It was thus suggested that absence of functional A30 gene may rescue from developing lupus nephritis in the patients. A30 is reported to be a potentially functional but rarely expressed Vk gene in humans. It is possible that normal B cells edit primarily rearranged A30 gene with autoreactive potentials by receptor editing mechanism for changing the affinity of the B cell Ag receptor to avoid self-reactivity, whereas SLE B cells may have a defect in this mechanism. Indeed, we found that normal B cells edit A30-Jk2 gene in their genome possibly by inversion mechanism, whereas SLE B cells contain rearranged A30-Jk2-Ck gene in the genome and express A30-associated mRNA, suggesting that receptor editing mechanism is also defective in patients with SLE. Our study suggests that polymorphism of Ig Vk locus, and failure of receptor editing may contribute to the development of pathogenic anti-DNA responses in humans.
Prevention of adoptively transferred diabetes in nonobese diabetic mice with IL-10-transduced islet-specific Th1 lymphocytes. A gene therapy model for autoimmune diabetes.
M Moritani, K Yoshimoto, S Ii, M Kondo, H Iwahana, T Yamaoka, T Sano, N Nakano, H Kikutani, M ItakuraAbstract | Full text | PDF (Page 1851)
Four pancreatic islet-specific CD4+ helper T (Th) 1 (Th1) clones and two Th1 clones transduced with an SRalpha promoter-linked murine IL-10 (mIL-10) cDNA of 2.0-6.0 x 10(6) cells were adoptively transferred to nonobese diabetic (NOD) mice at age 8 d. Cyclophosphamide (CY) was administered at age 37 d (plus CY), and the incidence of diabetes and the histological grade of insulitis were examined at age 47 d. After the adoptive transfer of IL-10-transduced Th1 cells, polymerase chain reaction (PCR) and reverse-transcription (RT)-PCR detected the neo gene and the retrovirus vector-mediated IL-10 mRNA in situ in recipient islets, respectively. RT-PCR detected the decrease of IFN-gamma mRNA relative to IL-10 mRNA in IL-10-transduced Th1 clones in vitro and also in recipient islets. All four wild type Th1 clones plus CY induced the insulitis grade of 2.75 and diabetes in 66% of recipient NOD mice. IL-10-transduced two Th1 clones plus CY induced periinsulitis with the grade of 1.43 and diabetes in 8.0%. The 1:1 mixture of wild type Th1 cells and IL-10-transduced Th1 cells plus CY induced periinsulitis with the grade of 1.85 and diabetes in 20%. The suppression of diabetes through decreasing IFN-gamma mRNA by the tissue-specific delivery of IL-10 to pancreatic islets with IL-10-transduced Th1 cells affords us the starting basis to develop the gene therapy for autoimmune diabetes.
Functional characterization of calcium-sensing receptor mutations expressed in human embryonic kidney cells.
S H Pearce, M Bai, S J Quinn, O Kifor, E M Brown, R V ThakkerAbstract | Full text | PDF (Page 1860)
The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that plays a key role in extracellular calcium ion homeostasis. We have engineered 11 CaR mutants that have been described in the disorders familial benign hypercalcemia (FBH), neonatal severe hyperparathyroidism (NSHPT), and autosomal dominant hypocalcaemia (ADH), and studied their function by characterizing intracellular calcium [Ca2+]i transients in response to varying concentrations of extracellular calcium [Ca2+]o or gadolinium [Gd3+]o. The wild type receptor had an EC50 for calcium (EC50[Ca2+]o) (the value of [Ca2+]o producing half of the maximal increase in [Ca2+]i) of 4.0 mM (+/- 0.1 SEM). However, five missense mutations associated with FBH or NSHPT, (P55L, N178D, P221S, R227L, and V817I) had significantly higher EC50[Ca2+]os of between 5.5 and 9.3 mM (all P < 0.01). Another FBH mutation, Y218S, had an EC50[Ca2+]o of > 50 mM but had only a mildly attenuated response to gadolinium, while the FBH mutations, R680C and P747fs, were unresponsive to either calcium or gadolinium. In contrast, three mutations associated with ADH, (F128L, T151M, and E191K), showed significantly reduced EC50[Ca2+]os of between 2.2 and 2.8 mM (all P < 0.01). These findings provide insights into the functional domains of the CaR and demonstrate that mutations which enhance or reduce the responsiveness of the CaR to [Ca2+]o cause the disorders ADH, FBH, and NSHPT, respectively.
Chimeric mice carrying 'regional' targeted deletion of the angiotensin type 1A receptor gene. Evidence against the role for local angiotensin in the in vivo feedback regulation of renin synthesis in juxtaglomerular cells.
T Matsusaka, H Nishimura, H Utsunomiya, J Kakuchi, F Niimura, T Inagami, A Fogo, I IchikawaAbstract | Full text | PDF (Page 1867)
We have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse (Agtr1a -/- <--> +/+) is made up of wild-type (Agtr1a +/+) cells or cells homozygous for Agtr1a deletion (Agtr1a -/-). In the latter, the AT1A coding exon was replaced with a reporter gene, lacZ. In Agtr1a -/- <--> +/+ mice, these two clones of cells are found to be clustered and display patchy distributions in the kidney and heart. Tracking of lacZ activities in hetero- (Agtr1a +/-) and homozygous (Agtr1a -/-) deletion mutant offspring from Agtr1a -/- <--> +/+ mice revealed that the promoter activity of Agtr1a is localized in JG cells, afferent arteriolar walls, glomerular mesangial region and endothelial cells, and apical and basolateral proximal tubule membranes. The JG apparatuses of Agtr1a -/- mice are markedly enlarged with intense expression of renin mRNA and protein. In Agtr1a -/- <--> +/+ mice, these changes were proportional to the degree of chimerism. Within a given Agtr1a -/- <--> +/+ mouse, however, the degree of JG hypertrophy/hyperplasia and the expression of renin mRNA and protein were identical between Agtr1a +/+ and Agtr1a -/- cells. Thus, in the in vivo condition tested, the local interaction between angiotensin and the AT1 receptor on the JG cells has little functional contribution to the feedback regulation of JG renin synthesis.
Dermal injection of immunocytes induces psoriasis.
Establishing direct and causal relationships among the confederacy of activated cell types present in psoriasis has been hampered by lack of an animal model. Within psoriatic plaques there are hyperplastic keratinocytes, infiltrating immunocytes, and activated endothelial cells. The purpose of this study was to determine if psoriasis is primarily a disorder of keratinocytes or the immune system. Using a newly developed experimental system in which full-thickness human skin is orthotopically transferred onto severe combined immunodeficient mice, autologous immunocytes were injected into dermis, and the resultant phenotype characterized by clinical, histologic, and immunophenotypic analyses. Engraftment of samples included both uninvolved/ symptomless (PN) skin removed from patients with psoriasis elsewhere, or from healthy individuals with no skin disease (NN skin). In 10 different experiments involving 6 different psoriasis patients, every PN skin was converted to a full-fledged psoriatic plaque skin by injection of autologous blood-derived immunocytes. In all but one psoriatic patient, the immunocytes required preactivation with IL-2 and superantigens to convert PN skin into psoriatic plaque skin. In every case, resultant plaques were characterized by visible presence of flaking and thickened skin, loss of the granular cell layer, prominent elongation of rete pegs with a dermal angiogenic tissue reaction, and infiltration within the epidermis by T cells. Lesional skin displayed 20 different antigenic determinants of the psoriatic phenotype. None of the four NN skin samples injected with autologous immunocytes converted to psoriatic plaques. We conclude that psoriasis is caused primarily by the ability of pathogenetic blood-derived immunocytes to induce secondary activation and disordered growth of endogenous cutaneous cells including keratinocytes and vascular endothelium.
Autoantibodies to nuclear envelope antigens in chronic fatigue syndrome.
K Konstantinov, A von Mikecz, D Buchwald, J Jones, L Gerace, E M TanAbstract | Full text | PDF (Page 1888)
We have identified and partially characterized the autoantibodies in sera of 60 patients with chronic fatigue syndrome. Approximately 52% of the sera were found to react with nuclear envelope antigens. The combination of nuclear rim staining observed in immunofluorescence microscopy and immunoblot analysis of highly purified nuclear envelope proteins provided initial characterization of these autoantibodies. Further characterization showed that some sera immunoprecipitated the in vitro transcription and translation product of a human cDNA clone encoding the nuclear envelope protein lamin B1. The autoantibodies were of the IgG isotype. The occurrence of autoantibodies to a conserved intracellular protein like lamin B1 provides new laboratory evidence for an autoimmune component in chronic fatigue syndrome.
Troglitazone inhibits vascular smooth muscle cell growth and intimal hyperplasia.
R E Law, W P Meehan, X P Xi, K Graf, D A Wuthrich, W Coats, D Faxon, W A HsuehAbstract | Full text | PDF (Page 1897)
Vascular smooth muscle cell (VSMC) proliferation and migration are responses to arterial injury that are highly important to the processes of restenosis and atherosclerosis. In the arterial balloon injury model in the rat, platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) are induced in the vessel wall and regulate these VSMC activities. Novel insulin sensitizing agents, thiazolidinediones, have been demonstrated to inhibit insulin and epidermal growth factor-induced growth of VSMCs. We hypothesized that these agents might also inhibit the effect of PDGF and bFGF on cultured VSMCs and intimal hyperplasia in vivo. Troglitazone (1 microM), a member of the thiazolidinedione class, produced a near complete inhibition of both bFGF-induced DNA synthesis as measured by bromodeoxyuridine incorporation (6.5+/-3.9 vs. 17.6+/-4.3% cells labeled, P < 0.05) and c-fos induction. This effect was associated with an inhibition (by 73+/-4%, P < 0.01) by troglitazone of the transactivation of the serum response element, which regulates c-fos expression. Inhibition of c-fos induction by troglitazone appeared to occur via a blockade of the MAP kinase pathway at a point downstream of MAP kinase activation by MAP kinase kinase. At this dose, troglitazone also inhibited PDGF-BB-directed migration of VSMC (by 70+/-6%, P < 0.01). These in vitro effects were operative in vivo. Quantitative image analysis revealed that troglitazone-treated rats had 62% (P < 0.001) less neointima/media area ratio 14 d after balloon injury of the aorta compared with injured rats that received no troglitazone. These results suggest troglitazone is a potent inhibitor of VSMC proliferation and migration and, thus, may be a useful agent to prevent restenosis and possibly atherosclerosis.
Ablation of the murine alpha myosin heavy chain gene leads to dosage effects and functional deficits in the heart.
W K Jones, I L Grupp, T Doetschman, G Grupp, H Osinska, T E Hewett, G Boivin, J Gulick, W A Ng, J RobbinsAbstract | Full text | PDF (Page 1906)
The alpha-myosin heavy chain (alpha-MyHC) is the major contractile protein expressed in the myocardium of adult mice. We have produced mice carrying a null mutation of alpha-MyHC by homologous recombination in murine ES cells. Homozygous null animals die between 11 and 12 d in utero of gross heart defects, while alpha-MyHC+/- heterozygotes survive and appear externally normal. The presence of a single functional alpha-MyHC+ allele in heterozygous animals results in reduced levels of the transcript and protein as well as fibrosis and alterations in sarcomeric structure. Examination of heart function using a working heart preparation revealed severe impairment of both contractility and relaxation in a subset of the alpha-MyHC+/- animals. Thus, two alpha-MyHC+ alleles are necessary for normal cardiac development, and hemizygosity for the normal allele can result in altered cardiac function.
Processing and proliferative effects of human progastrin in transgenic mice.
T C Wang, T J Koh, A Varro, R J Cahill, C A Dangler, J G Fox, G J DockrayAbstract | Full text | PDF (Page 1918)
Incompletely processed gastrins have been postulated to play a role in growth of the gastrointestinal tract, but few studies have examined the effects of progastrin on mucosal proliferation in vivo. Human gastrin gene expression and progastrin processing were therefore studied in transgenic mice containing a human gastrin (hGAS) minigene, and compared to processing in mice bearing an insulin gastrin (INS-GAS) transgene that overexpresses amidated gastrin. Progastrin processing was studied using region-specific antisera and radioimmunoassays, biosynthetic labeling, immunoprecipitation, and HPLC. Proliferative effects due to overexpression of processed and unprocessed gastrin in INS-GAS and hGAS mice, respectively, were determined using routine histology and BrdU incorporation. The pancreatic islets of INS-GAS mice were able to produce carboxyamidated G-17, resulting in a twofold elevation of serum amidated gastrin, marked thickening of the oxyntic mucosa, and an increased BrdU labeling index (LI) of the gastric body. In contrast, livers of adult hGAS mice expressed abundant human gastrin mRNA and human progastrin but were unable to process this peptide to the mature amidated form, resulting in markedly elevated serum progastrin levels and normal amidated gastrin levels. Nevertheless, there was a marked increase in the BrdU labeling index of the colon in hGAS mice (LI 7.46+/-1.90%), as well as in INS-GAS mice (LI 6.16+/-1.17%), compared to age-matched, wild type control mice (LI 4.01+/-0.98%, P < 0.05). These studies suggest that incompletely processed gastrin precursors may contribute to colonic mucosal proliferation in vivo.
150-kD oxygen-regulated protein is expressed in human atherosclerotic plaques and allows mononuclear phagocytes to withstand cellular stress on exposure to hypoxia and modified low density lipoprotein.
Y Tsukamoto, K Kuwabara, S Hirota, J Ikeda, D Stern, H Yanagi, M Matsumoto, S Ogawa, Y KitamuraAbstract | Full text | PDF (Page 1930)
The 150-kD oxygen-regulated protein (ORP150) was initially characterized based on its selective expression in astrocytes subjected to oxygen deprivation (Kuwabara, K., M. Matsumoto, J. Ikeda, O. Hori, S. Ogawa, Y. Maeda, K. Kitagawa, N. Imuta, K. Kinoshita, D.M. Stern, et al. 1996. J. Biol. Chem. 279:5025-5032). We have found that exposure of cultured human aortic smooth muscle cells and mononuclear phagocytes (MPs) to hypoxia (pO2 approximately 12-14 torr) induces ORP150 transcripts and production of the antigen, whereas incubation with either hydrogen peroxide, sodium arsenite, heat shock, or 2-deoxyglucose was without effect. Tissue extracts prepared from human atherosclerotic lesions demonstrated expression of ORP150 mRNA and antigen, vs lack of ORP150 in samples from nonatherosclerotic areas. In situ hybridization using ORP150 riboprobes showed the mRNA to be predominantly [correction of predominately] present in macrophages in in atherosclerotic plaques. Furthermore, autoantibody to ORP150 was demonstrated in the serum of patients with severe atherosclerosis, consistent with inducible in vivo expression of ORP150. Introduction of antisense oligonucleotide for ORP150 selectively diminished hypoxia-mediated induction of ORP150 antigen and reduced the viability of hypoxic MPs, especially in the presence of modified (oxidized/acetylated) LDL. In support of a role for ORP150 in the MPs' response to the microenvironment of an atheroma, the presence of oxidized LDL enhanced by approximately 10-fold ORP150 expression in hypoxic cultures. These data indicate that cells of the atherosclerotic vessel wall express ORP150 as part of a protective mechanism, potentially triggered by local hypoxia/hypoxemia and augmented by modified lipoproteins. The presence of antibody to ORP150 in sera of patients with severe atherosclerosis emphasizes the possibility that ORP150 may be a marker of vascular pathology.