Elevated levels of the complement components C3 and factor B in ventricular cerebrospinal fluid of patients with traumatic brain injury

Immunological events occurring in the central nervous system (CNS) as a result of head trauma are largely unexplored. We report here that the levels of the alternative pathway complement proteins C3 and factor B are elevated in the cerebrospinal fluid (CSF) of head-injured patients. C3 and factor B indices suggest that changes in C3 and factor B levels in CSF are most likely due to altered blood-brain barrier integrity and not to intrathecal synthesis. These data demonstrate, for the first time, elevated levels of complement proteins in CSF of patients with severe traumatic brain injury. Elevated complement levels in brain injury may contribute to secondary damage.

Enhanced expression of chemotactic receptors in multiple sclerosis lesions

We have previously shown that astrocytes and microglia express the receptors for C5a, interleukin-8 (IL-8) and N-formyl-Met-Leu-Phe (FMLP) in vitro. The expression and function of chemotactic receptors in the central nervous system (CNS) is, however, largely unexplored. In this study, we examined tissue sections from normal human brain and active, chronic active and chronic silent multiple sclerosis (MS) lesions for the expression of the receptors for C5a, IL-8 and FMLP by immunohistochemistry. In normal brain tissue, the expression of all three receptors was seen at low levels on astrocytes and microglia. In contrast, expression for all three receptors was markedly elevated on foamy macrophages in the acute and chronic active MS lesions. In addition, fibrous astrocytes stained intensely for the C5a receptor in the chronic active disease. Receptor expression in the chronic silent lesion was low and similar to that seen in normal brain, with staining confined to a few hypertrophic astrocytes and foamy macrophages. These are the first studies to demonstrate expression of these receptors in the CNS and elevated receptor expression in inflammatory MS lesions. The data suggest that these chemotactic receptors may play a role in inflammatory responses in MS and possibly in other CNS diseases.

Chronic complement C3 gene expression in the CNS of transgenic mice with astrocyte-targeted interleukin-6 expression

Both cytokines and complement are thought to play significant, but poorly understood roles, in the pathogenesis of a variety of neurodegenerative diseases. In this study, we examined the expression of C3, the central component of complement, in the brains of transgenic mice with constitutive astrocyte expression of the proinflammatory cytokine, interleukin-6 (IL-6). Immunohistochemistry studies demonstrated elevated deposition of C3 in the brains of transgenic animals compared with normal animals. Northern blot analysis of mRNA from brain and other tissues demonstrated an age-related increase in C3 gene expression only in the brains of transgenic animals, indicative of local synthesis. In situ hybridization studies revealed coincidence between C3 and IL-6 transgene expression, as well as areas of neuronal and white matter damage observed in cerebellum and hind brain. Furthermore, C3 mRNA expression was observed in ependymal cells, perivascular mononuclear cells, endothelial cells, and scattered cells throughout the white matter and the brain stem. The overlap in C3 mRNA expression with areas of pathology suggests that complement may contribute to the inflammation and cellular injury observed in this model. The transgenic mice used in these studies provide a novel and valuable tool for examining the role of complement in central nervous system pathobiology.

Transforming growth factor-beta2-mediated regulation of C3 gene expression in monocytes

In this report, we show that transforming growth factor-beta2 (TGF-beta2) regulates C3 gene expression in the human monocyte cell lines, U937 and THP-1, and human peripheral blood monocytes. Treatment of U937 or THP-1 cells with TGF-beta2 resulted in a dose-dependent induction of C3 protein and mRNA expression. Dose-dependent increases of C3 protein and mRNA levels were also detected in TGF-beta2-treated primary blood monocytes, demonstrating that TGF-beta2 can modulate C3 expression in nontransformed monocytes. Kinetic analysis demonstrated that TGF-beta2-mediated induction of C3 mRNA and protein could be detected within 8 hr, and the induction was continuous up to 72 hr. Exposure of cells to TGF-beta2 for as little as 2 hr was sufficient to induce C3 expression. TGF-beta2 did not significantly increase C3 mRNA stability as determined by mRNA half-life studies. Collectively, our results demonstrate that TGF-beta2 regulates the expression of C3 in monocytes and suggest that TGF-beta2 may play a role in modulating the synthesis of C3 during inflammatory responses.

Differential regulation of C3 gene expression in human astroglioma cells by interferon-gamma and interleukin-1 beta

In this report, we examined interferon-gamma (IFN-gamma) and interleukin-1 beta (IL-1 beta)-mediated regulation of the expression of C3, the third component of complement, in a human astroglioma cell line. Interleukin-1 beta induced C3 protein expression ten-fold more rapidly than IFN-gamma. De novo protein synthesis was required for IFN-gamma to stimulate C3 expression, while cycloheximide and IL-1 beta treatment of cells markedly increased C3 expression. Actinomycin D, inhibited C3 gene induction by IFN-gamma and IL-1 beta suggesting that these cytokines act, in part, at the transcriptional level to enhance C3 expression. Understanding cytokine-mediated regulation of complement gene expression in the astrocyte is important in defining the role of these molecules in CNS inflammation and autoimmune diseases.

Expression of the receptors for the C5a anaphylatoxin, interleukin-8 and FMLP by human astrocytes and microglia

The expression of chemotactic receptors in the central nervous system is largely unexplored. In this study, we examined human astrocytes and microglia as well as the conditionally immortalized human astrocyte cell line HSC2 for expression of the C5a-anaphylatoxin receptor (C5aR), the interleukin-8 receptor (IL-8R) and the f-Met-Leu-Phe receptor (FMLPR). Using flow cytometry, indirect immunofluorescence and RT-PCR analysis, we demonstrated that astrocytes, microglia and HSC2 cells contain specific RNA and express surface protein for all three chemotactic receptors. These are the first studies to demonstrate definitively the expression of these chemotactic receptors astrocytes and microglia, thereby expanding the types of cells known to express chemotactic receptors. Moreover, these data suggest that these chemotactic receptors may play an important role in mediating the inflammatory response and perhaps other yet undescribed biological phenomena in the central nervous system.

Complement biosynthesis in the central nervous system

Complement is an important effector arm of the human immune response. Binding of proteolytic fragments derived from activation of complement by specific receptors leads to responses as diverse as inflammation, opsonization, and B-cell activation. The importance of characterizing the expression and regulation of complement in the CNS is highlighted by growing evidence that complement plays a significant role in the pathogenesis of a variety of neurological diseases, such as multiple sclerosis and Alzheimer's disease. In vitro studies have demonstrated that astrocytes, the predominant glial cell type in the brain, are capable of expressing or producing a majority of the components of the complement system. Expression of many complement proteins synthesized by astrocytes is regulated by both pro- and anti-inflammatory cytokines, many of which are also produced by several cell types in the CNS. In addition to astrocytes, ependymal cells, endothelial cells, microglia, and neurons have recently been shown to synthesize various complement proteins or express complement receptors on their cell surfaces. Together, these studies demonstrate that several cell types throughout the brain have the potential to express complement and, in many cases, increase expression in response to mediators of the acute phase response. These studies suggest that complement may play a greater role in CNS immune responses than previously thought, and pave the way for better understanding of the dynamics of complement expression and regulation in vivo. Such understanding may lead to therapeutic manipulation of complement host defense functions in a variety of inflammatory and degenerative diseases in the CNS.

Transforming growth factor-beta 1 inhibits inflammatory cytokine-induced C3 gene expression in astrocytes

In this report, we show that transforming growth factor-beta (TGF-beta) can significantly inhibit the capacity of IFN-gamma, IL-1 beta, and TNF-alpha to augment expression of the central component of complement C3 in the human astroglioma cell line D54-MG. Treatment of D54-MG cells with TGF-beta alone had no dose- or time-dependent effect on basal C3 protein or mRNA levels. However, TGF-beta suppressed induction of C3 expression at both the protein and mRNA level in D54-MG cells treated with inflammatory cytokines. The extent of TGF-beta-mediated suppression was cytokine-specific, and suppression of protein production did not necessarily correspond to reductions in steady-state mRNA levels for each cytokine. Similar findings were obtained at the mRNA level using primary rat astrocytes, indicating that TGF-beta can modulate C3 gene expression in nontransformed astrocytic cells. Kinetic studies demonstrated that TGF-beta mediates its suppressive effect for at least 72 h, and that pretreatment of cells with TGF-beta for as little as 2 h significantly reduced the ability of all three inflammatory cytokines to enhance C3 expression. Our results suggest that TGF-beta may play an important role in modulating the endogenous synthesis of complement by astrocytes under inflammatory conditions.

Transforming growth factor-beta 1 inhibits inflammatory cytokine-induced C3 gene expression in astrocytes

In this report, we show that transforming growth factor-beta (TGF-beta) can significantly inhibit the capacity of IFN-gamma, IL-1 beta, and TNF-alpha to augment expression of the central component of complement C3 in the human astroglioma cell line D54-MG. Treatment of D54-MG cells with TGF-beta alone had no dose- or time-dependent effect on basal C3 protein or mRNA levels. However, TGF-beta suppressed induction of C3 expression at both the protein and mRNA level in D54-MG cells treated with inflammatory cytokines. The extent of TGF-beta-mediated suppression was cytokine-specific, and suppression of protein production did not necessarily correspond to reductions in steady-state mRNA levels for each cytokine. Similar findings were obtained at the mRNA level using primary rat astrocytes, indicating that TGF-beta can modulate C3 gene expression in nontransformed astrocytic cells. Kinetic studies demonstrated that TGF-beta mediates its suppressive effect for at least 72 h, and that pretreatment of cells with TGF-beta for as little as 2 h significantly reduced the ability of all three inflammatory cytokines to enhance C3 expression. Our results suggest that TGF-beta may play an important role in modulating the endogenous synthesis of complement by astrocytes under inflammatory conditions.

Expression of decay-accelerating factor (CD55), membrane cofactor protein (CD46) and CD59 in the human astroglioma cell line, D54-MG, and primary rat astrocytes

In this report, we have shown the expression of the complement regulatory proteins decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46) and CD59 on human D54-MG astroglioma cells by several methods, including immunofluorescence, flow cytometry and Western blotting and Northern blot analysis. These studies demonstrate that all three proteins are structurally and antigenically similar to their counterparts expressed on HepG2 and SW480 cells (hepatocyte and epithelial cell lines, respectively). D54-MG cells express mRNA for all three proteins of the appropriate size(s). The phosphatidylinositol-specific enzyme, PIPLC, cleaved DAF from the surface of D54-MG cells, demonstrating that DAF is linked by a glycophospholipid anchor as has been shown for other cell types. Flow cytometry demonstrates that primary rat astrocytes also constitutively express all three regulatory proteins. These data are the first to demonstrate the expression of CD59 on astrocytes, and the presence of all three regulatory proteins on astrocytes suggests that regulation of complement activation in the central nervous system is important in neural host defense mechanisms.

Interleukin-1 and tumor necrosis factor-mediated regulation of C3 gene expression in human astroglioma cells

In this report, we show that in the human astroglioma cell line D54-MG, both interleukin-1 (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) enhance C3 gene expression in a time- and dose-dependent manner. Kinetic analysis demonstrates that after 96 h, C3 mRNA levels increase approximately 30-fold and 20-fold in response to IL-1 beta or TNF-alpha, respectively. C3 protein production increases proportionally, reaching levels 36-fold and 18-fold higher than untreated controls upon exposure to IL-1 beta or TNF-alpha, respectively. D54-MG cells require a minimal 1 h exposure to IL-1 beta in order to enhance C3 gene expression significantly, while 4 to 8 h are required for TNF-alpha. Simultaneous treatment of D54-MG cells with IL-1 beta and interferon-gamma (IFN-gamma) resulted in an additive increase in both C3 mRNA and protein expression, a finding not seen with the combination of TNF-alpha and IFN-gamma. Primary rat astrocytes also express increased C3 mRNA levels after 48 h in response to IL-1 beta (5.3-fold increase) and TNF-alpha (7-fold increase), while an additive effect was observed upon simultaneous treatment with both IL-1 beta and IFN-gamma. In the central nervous system (CNS), endogenous complement and cytokine production by astrocytes, and enhancement by IFN-gamma, a product of activated T cells often seen in the CNS in neural autoimmune disease, may contribute to the pathogenesis of inflammatory demyelinating diseases such as multiple sclerosis.

Production and interferon-gamma-mediated regulation of complement component C2 and factors B and D by the astroglioma cell line U105-MG

In this paper, we demonstrate the synthesis of the complement component C2 and factors B and D by the human astroglioma cell line U105-MG. All three components were structurally and antigenically similar to their serum counterparts, as determined by biosynthetic labelling studies or Western blot analysis. Northern blot analysis demonstrated that the mRNAs of all three components had the same apparent sizes as the equivalent mRNAs from hepatocyte and monocyte cell lines. Interestingly, U105-MG cells produce two C2 transcripts with sizes of approximately 2.8 and 2.3 kb. Interferon-gamma (IFN-gamma) enhanced the expression of C2 and factor B mRNA and protein in a dose- and time-dependent fashion, while factor D expression was refractory to IFN-gamma. IFN-gamma appeared to predominantly enhance the expression of the large (2.8 kb) C2 transcript. Kinetic studies demonstrated peak C2 and factor B expression in 48 h in response to IFN-gamma, similar to the acute-phase response of factor B in serum. These data are the first to demonstrate the synthesis of C2 and factor D by astroglioma cells. Combined with previous reports documenting the synthesis of C3 by astrocytes, our data suggest that endogenous synthesis of complement proteins, and particularly of alternative pathway activation components (C3, factors B and D), may play an important role in host defence in the central nervous system.

Purification and characterization of 3-ketoacyl-acyl carrier protein synthase III from spinach. A condensing enzyme utilizing acetyl-coenzyme A to initiate fatty acid synthesis

The 3-ketoacyl-acyl carrier protein (ACP) synthase III from spinach was purified to homogeneity by an eight-step procedure that included an ACP-affinity column. The size of the native enzyme was M(r) = 63,000 based on gel filtration, and its subunit size was M(r) = 40,500 based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that 3-ketoacyl-ACP synthase III may be a homodimer. The purified enzyme was highly specific for acetyl-CoA and malonyl-ACP. The Km for acetyl-CoA was 5 microM when assayed in the presence of 10 microM malonyl-CoA. Acetyl-, butyryl-, and hexanoyl-ACP would not substitute for acetyl-CoA as substrates. The specificity for acetyl-CoA suggested that the physiological function of 3-ketoacyl-ACP synthase is to catalyze the initial condensation reaction in fatty acid biosynthesis. The homogeneous 3-ketoacyl-ACP synthase was capable of catalyzing acetyl-CoA:ACP transacylation but at a rate about 90-fold slower than the condensation reaction with malonyl-ACP. The 3-ketoacyl-ACP synthase was inhibited 100% by 5 mM N-ethylmaleimide or 20 mM sodium arsenite.

DNA sequence and analysis of a cryptic 4.2-kb plasmid from the filamentous cyanobacterium, Plectonema sp. strain PCC 6402

The 4194-bp plasmid, pRF1, from Plectonema sp. Strain PCC 6402 was completely sequenced and analyzed. Seven potential open reading frames were identified. The predicted amino acid sequence of open reading frame C (ORF C) had identities of 34, 29, and 25% with Rep B from the Staphylococcus aureus plasmid, pUB110; Rep from the Bacillus amyloliquefaciens plasmid, pFTB14; and protein A from the S. aureus plasmid, pC194, respectively. A 75-amino-acid region conserved in these proteins (Rep B, Rep, and protein A) also was highly conserved in ORF C with identities of 45, 37, and 40%, respectively. Significantly, 16 of the 21 amino acids conserved in Rep B, Rep, and protein A were found at the same positions in ORF C. This ORF may encode a replication protein that includes a region conserved in some eubacteria. Additional structural features include a 425-bp region that contains palindromes, tandem repeats, and short direct repeats which may correspond to the origin of replication. An 18-bp inverted repeat was located between two open reading frames, A and G.

Interferon-gamma regulation of C3 gene expression in human astroglioma cells

In this report, we show that the human astroglioma cell line, D54-MG, constitutively expresses C3 mRNA and secretes antigenically detectable C3 protein. The cytokine interferon-gamma (IFN-gamma) enhances C3 mRNA and protein expression by D54-MG cells in a dose- and time-dependent manner. C3 mRNA from both D54-MG cells and primary human adult astrocytes has the same apparent size (5.1-5.2 kb) as C3 mRNA from hepatocyte and monocyte cell lines. Constitutive C3 mRNA levels in D54-MG cells and primary human astrocytes are comparable. Primary rat astrocytes also constitutively express C3 mRNA, which is enhanced upon exposure to IFN-gamma. These data are novel since expression of C3 in other cell types is refractory to IFN-gamma. In the central nervous system (CNS), endogenous complement production by astrocytes, and enhancement by the cytokine IFN-gamma, may contribute to the pathogenesis of inflammatory demyelinating diseases such as multiple sclerosis (MS).

Purification and characterization of acyl carrier protein from two cyanobacteria species

The acyl carrier protein (ACP), an essential protein cofactor for fatty acid synthesis, has been isolated from two cyanobacteria: the filamentous, heterocystous, Anabaena variabilis (ATCC 29211) and the unicellular Synechocystis 6803 (ATCC 27184). Both ACPs have been purified to homogeneity utilizing a three-column procedure. Synechocystis 6803 ACP was purified 1800-fold with 67% yield, while A. variabilis ACP was purified 1040-fold with 50% yield. Yields of 13.0 micrograms ACP/g Synechocystis 6803 and 9.0 micrograms ACP/g A. variabilis were achieved. Amino acid analysis indicated that these ACPs were highly charged acidic proteins similar to other known ACPs. Sequence analysis revealed that both cyanobacterial ACPs were highly conserved with both spinach and Escherichia coli ACP at the phosphopantetheine prosthetic group region. Examining the probability of alpha-helix and beta-turn regions in various ACPs, showed that cyanobacterial ACPs were more closely related to E. coli ACP than spinach ACP I. Immunoblot analysis and a competitive binding assay for ACP illustrated that both ACPs bound poorly to spinach ACP I antibody. SDS/PAGE and native PAGE of Synechocystis 6803 ACP and A. variabilis ACP showed that cyanobacteria ACPs co-migrated with E. coli ACP and had relative molecular masses of 18,100 and 17,900 respectively. Both native and urea gel analysis of acyl-ACP products from fatty acid synthase reactions demonstrated that bacterial ACPs and plant ACP gave essentially the same metabolic products when assayed using either bacterial or plant fatty acid synthase. A. variabilis and Synechocystis 6803 ACP could be acylated using E. coli acyl ACP synthetase.

C4b-binding protein, a regulatory component of the classical pathway of complement, is an acute-phase protein and is elevated in systemic lupus erythematosus

A radioimmunoassay using monoclonal and polyclonal antihuman C4b-binding protein (C4BP) antibody was developed to quantitate C4BP in serum. Using the assay, the levels of C4BP in healthy individuals, in patients with systemic lupus erythematosus (SLE), and in acute-phase individuals were determined. The levels of C4BP are significantly elevated in individuals with SLE (186%; p = 0.0001) and are even higher in individuals during the acute phase (286%; p = 0.0001). To confirm whether or not individuals were in the acute-phase response, serum C-reactive protein (CRP) levels were assessed. In the acute-phase response, CRP levels were 100-fold elevated over normals, but did not correlate with increases in C4BP (r = -0.031; p = 0.899). In SLE patients, the CRP levels were significantly, but moderately, elevated (5-fold; p = 0.028). The data indicate that C4BP is an acute-phase reactant and is differentially regulated from CRP during the acute-phase response.

Molecular analysis of the murine C4b-binding protein gene. Chromosome assignment and partial gene organization

Murine C4b-binding protein (C4BP) is a regulatory molecule in the classical pathway of complement. C4BP is composed predominantly of short consensus repeats (SCRs) approximately 60 amino acids in length, which contain a framework of conserved residues. The SCRs are found in many complement molecules and a growing number of noncomplement molecules as well and are a major structural feature of some of these molecules. To characterize the structure of the murine C4BP gene, a cosmid library constructed from Balb/c liver DNA was screened. Several nearly identical, overlapping clones were identified; however, none of the clones, alone or in combination, covered the entire C4BP gene. One clone (D26) was chosen for detailed analysis and found to contain all but the leader region, the first SCR, and the first half of the second SCR. The SCRs three through six were each encoded by single exons. Only the latter half of the second SCR was present on the clone, and it was encoded by a single exon, demonstrating that murine C4BP has a split SCR at the genomic level. Structural mapping of this portion of the gene demonstrates that the region extending from the second half of the second SCR through the nonrepeat and untranslated region spans approximately 12 kb; however, genomic Southern blot analysis suggests that the gene is between 20 and 30 kb in length. Analysis of the 3' genomic sequence demonstrates that this region of the gene has homology with SV-40 late (class II) RNA sequences. These sequences may play a role in 3' cleavage of the precursor RNA prior to polyadenylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Complete intron/exon organization of DNA encoding the alpha' chain of human C3

The third component of human complement (C3), a central molecule in both the classical and alternative pathways of complement, is comprised of two polypeptides, termed the alpha and beta chains. Activation of C3 cleaves the alpha chain into two fragments, C3a, an inflammatory peptide, and the alpha' chain which remains covalently linked to the beta chain. Proteolytic fragments derived from the alpha' chain during activation and regulation of complement play a significant role in host defense and regulation of the immune response. Two cosmid clones covering the alpha' chain region were used to characterize the structure of this portion of the C3 gene. The alpha' chain is encoded by 24 exons, which range in size from 52 to 213 base pairs (bp) with an average size of 115 bp. The splice donor sequence at the beginning of intron 12 has a rare sequence variant of GC instead of the usual GT sequence. Ten introns have been completely sequenced and were surprisingly short, ranging in size from 85 to 242 bp with an average of 140 bp. Other introns range in size from 250 bp to over 4 kilobases in length. The gene size for this portion of C3 is estimated to be 23-24 kilobases. Comparison of exon structure with protein domains and with peptide mapping studies demonstrates that several binding sites on C3 are encoded by single exons. These data support the hypothesis that individual exons can code for functional protein domains.

A Cerulenin Insensitive Short Chain 3-Ketoacyl-Acyl Carrier Protein Synthase in Spinacia oleracea Leaves

A cerulenin insensitive 3-ketoacyl-acyl carrier protein synthase has been assayed in extracts of spinach (Spinacia oleracea) leaf. The enzyme was active in the 40 to 80% ammonium sulfate precipitate of whole leaf homogenates and catalyzed the synthesis of acetoacetyl-acyl carrier protein. This condensation reaction was five-fold faster than acetyl-CoA:acyl carrier protein transacylase, and the initial rates of acyl-acyl carrier protein synthesis were independent of the presence of cerulenin. In the presence of fatty acid synthase cofactors and 100 micromolar cerulenin, the principal fatty acid product of de novo synthesis was butyric and hexanoic acids. Using conformationally sensitive native polyacrylamide gel electrophoresis for separation, malonyl-, acetyl-, butyryl-, hexanoyl, and long chain acyl-acyl carrier proteins could be detected by immunoblotting and autoradiography. In the presence of 100 micromolar cerulenin, the accumulation of butyryl- and hexanoyl-acyl carrier protein was observed, with no detectable long chain acyl-acyl carrier proteins or fatty acids being produced. In the absence of cerulenin, the long chain acyl-acyl carrier proteins also accumulated.