Apoprotein E is synthesized and secreted by resident and thioglycollate-elicited macrophages but not by pyran copolymer- or bacillus Calmette-Guerin-activated macrophages

Multi-omics profiling identifies C1QA/B+ macrophages with multiple immune checkpoints associated with esophageal squamous cell carcinoma (ESCC) liver metastasis

Background

Esophageal squamous cell carcinoma (ESCC) is a highly lethal malignant tumor lacking effective treatments; 20% of ESCC patients develop liver metastasis with an extremely short survival time of ≈5 months. The tumor microenvironment (TME) plays a crucial role in tumor homeostasis, but the relationship between the ESCC TME and liver metastasis is still unknown.

Methods

To identify potential cell populations contributing to ESCC liver metastasis, single-cell RNA (scRNA) sequencing data were analyzed to identify the major cell populations within the TME. Each of the major cell populations was re-clustered to define detailed cell subsets. Thereafter, the gene set variation analysis (GSVA) score was calculated for the bulk RNA-seq data based on the gene signatures of each cell subset. The relationship between the GSVA score of each cellular subset and clinical outcome was further analyzed to identify the cellular subset associated with ESCC liver metastasis, which was validated by multiplex immunohistochemistry.

Results

C1QA/B⁺ tumor-associated macrophages (TAMs) acted as the central regulator of the ESCC TME, closely associated with several key cell subsets. Several immune checkpoints, including CD40, CD47 and LGALS9, were all positively expressed in C1QA/B⁺ macrophages, which may exert central regulatory control of immune evasion by ESCC via these immune checkpoints expressions.

Conclusions

Our results comprehensively revealed the landscape of tumor-infiltrating immune cells associated with ESCC prognosis and metastasis, and suggest a novel strategy for developing immunotherapies for ESCC liver metastasis by targeting C1QA/B⁺ TAMs.

Apolipoprotein E variants correlate with the clinical presentation of paediatric inflammatory bowel disease: A cross-sectional study

BACKGROUND

It has been suggested that apolipoprotein E (APOE) polymorphisms are associated with the risk of developing inflammatory bowel disease (IBD) and the early age of disease onset. However, there are no reports regarding the relationship with clinical characteristics and disease severity.

AIM

To summarise that APOE polymorphisms are associated with the risk of developing IBD and the early age of disease onset.

METHODS

In total, 406 patients aged 3-18 with IBD (192 had ulcerative colitis and 214 had Crohn’s disease) were genotyped using the TaqMan hydrolysis probe assay. Clinical expression was described at diagnosis and the worst flare by disease activity scales, albumin and C-reactive protein levels, localisation and behaviour (Paris classification). Systemic steroid intake with the total number of courses, immunosuppressive, biological, and surgical treatment with the time and age of the first intervention were determined. The total number of exacerbation-caused hospitalisations, the number of days spent in hospital due to exacerbation, the number of relapses, and severe relapses were also estimated.

RESULTS

Ulcerative colitis patients with the APOEε4 allele had lower C-reactive protein values at diagnosis (P = 0.0435) and the worst flare (P = 0.0013) compared to patients with the APOEε2 allele and genotype APOEε3/ε3. Crohn’s disease patients with the APOEε2 allele scored lower on the Pediatric Crohn’s Disease Activity Index at diagnosis (P = 0.0204). IBD patients with APOEε2 allele spent fewer days in the hospital due to relapse (P = 0.0440).

CONCLUSION

APOE polymorphisms are associated with the risk of developing IBD and the clinical expression of IBD. However, the clinical relevance of the differences identified is rather modest.

Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational

HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.

Changes in the NMR metabolic profile of human microglial cells exposed to lipopolysaccharide or morphine

Microglial cells play a major role in host defense of the central nervous system. Once activated, several functional properties are up-regulated including migration, phagocytosis, and secretion of inflammatory mediators such as cytokines and chemokines. Little, if anything, is known about the metabolic changes that occur during the activation process. High-resolution (1)H nuclear magnetic resonance spectra obtained from perchloric acid extracts of human microglial cell cultures exposed to lipopolysaccharide (LPS) or morphine were used to both identify and quantify the metabolites. We found that human microglia exposed to LPS had increased concentrations of glutamate and lactate, whereas the cells exposed to morphine had decreased concentrations in creatinine, taurine, and thymine. Glutamate and creatinine were the key metabolites differentiating between the two stimuli. These results are discussed in terms of activation and differences in the inflammatory response of human microglial cells to LPS and morphine.

The immune-modulatory role of apolipoprotein E with emphasis on multiple sclerosis and experimental autoimmune encephalomyelitis

Apolipoprotein E (apoE) is a 34.2 kDa glycoprotein characterized by its wide tissue distribution and multiple functions. The nonlipid-related properties of apoE include modulating inflammation and oxidation, suppressing T cell proliferation, regulating macrophage functions, and facilitating lipid antigen presentation by CD1 molecules to natural killer T (NKT) cells, and so forth. Increasing studies have revealed that APOE ε allele might be associated with multiple sclerosis (MS), although evidence is still not sufficient enough. In this review, we summarized the current progress of the immunomodulatory functions of apoE, with special focus on the association of APOE ε allele with the clinical features of MS and of its animal model experimental autoimmune encephalomyelitis (EAE).

The role of apolipoprotein E in Guillain-Barré syndrome and experimental autoimmune neuritis

Apolipoprotein E (apoE) is a 34.2 kDa glycosylated protein characterized by its wide tissue distribution and multiple functions. ApoE has been widely studied in lipid metabolism, cardiocerebrovascular diseases, and neurodegenerative diseases like Alzheimer's disease and mild cognitive impairment, and so forth. Recently, a growing body of evidence has pointed to nonlipid related properties of apoE, including suppression of T cell proliferation, regulation of macrophage function, facilitation of lipid antigen presentation by CD1 molecules to natural killer T (NKT) cells, and modulation of inflammation and oxidation. By these properties, apoE impacts physiology and pathophysiology at multiple levels. The present paper summarizes updated studies on the immunoregulatory function of apoE, with special focus on isoform-specific effects of apoE on Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN).

The cell and molecular biology of apolipoprotein E synthesis by macrophages

Mononuclear phagocytes secrete over 50 different proteins that are regulated during differentiation and that are under the influence of various materials and factors in their extracellular milieu as part of the inflammatory response. The complex nature of the regulation of the expression of these molecules is displayed by apolipoprotein E (ApoE). ApoE mRNA first appears as monocytes differentiate into macrophages, and this expression is paralleled by the secretion of ApoE by the cells. In mature macrophages ApoE synthesis and secretion are decreased by activation of macrophages with endotoxin and interferon-gamma. Although these macrophages contain abundant translatable ApoE mRNA, little ApoE is synthesized, suggesting that this decrease occurs largely at the translational level. ApoE is also controlled at the level of secretion. ApoE is concentrated in the Golgi complex of macrophages and is also found in endoplasmic reticulum, secretion vesicles and coated vesicles. When macrophages come in contact with immune complexes the intracellular ApoE compartment degranulates rapidly. Therefore, ApoE is regulated at the levels of secretion, translation and transcription.

Inflammatory signaling pathways regulating ApoE gene expression in macrophages

The atheroprotective role of apolipoprotein E (apoE) is well established. During inflammation, expression of apoE in macrophages is reduced leading to enhanced atheromatous plaque development. In the present study, we investigated the signaling pathways involved in the repression of apoE gene expression in response to lipopolysaccharide (LPS) treatment, a condition that mimics the inflammatory stress, in mouse macrophages RAW 264.7. We identified Tpl-2 and MEKK1 as the kinases that are primarily responsible for the down-regulation of apoE promoter activity by LPS. Using a dominant negative form of IkappaB, we established that Tpl-2 and MEKK1 signaling pathways converge to NF-kappaB acting on the apoE core promoter -55/+73. In addition to NF-kappaB activation, LPS also activated c-Jun via its phosphorylation by JNK. The activity of the apoE promoter was repressed by c-Jun, whereas small interference RNA-mediated inhibition of endogenous c-Jun expression reversed the inhibitory effect of Tpl-2 on the apoE promoter. Transfection experiments and DNA binding assays showed that the binding site for c-Jun is in the -55/+73 region of the apoE promoter. Finally, we showed that LPS inhibited apoE gene expression via activation of the Tpl-2/MEK/ERK pathway acting on a different apoE promoter region. In summary, LPS represses apoE gene expression in macrophages via signaling pathways that involve the upstream kinases Tpl-2 and MEKK1, the intermediate mitogen-activated protein kinases ERK and JNK, and the downstream transcription factors AP-1 and NF-kappaB that inhibit the apoE promoter activity via distinct regions.

Apoprotein E isoform-dependent expression and secretion of pro-inflammatory cytokines TNF-alpha and IL-6 in macrophages

The anti-atherogenic properties of human apoprotein E-associated lipoproteins have been partially attributed to its anti-inflammatory properties. We studied if endogenously expressed apoprotein E (apoE) elicits isoform-dependent effects on pro-inflammatory cytokine expression and secretion. Mouse J774A.1 peritoneal macrophages without native expression of apoE were used to establish cell lines with stable expression of the three human apoE isoforms, apoE2, apoE3 and apoE4. In the presence of lipopolysaccharide (LPS), expression and secretion of TNF-alpha and IL-6 in cells expressing different apoE isoforms were determined by RT-PCR, immunoblotting and ELISA assays. ApoE3-expressing cells have significantly lower expression and secretion levels of the two cytokines as compared to cells with apoE2 and apoE4 expression. Such observations were accompanied with the lowest ERK1/2 activity in apoE3-expressing cells. Further study shows that the apoE isoform-dependent variations of TNF-alpha and IL-6 expression/secretion in macrophages are diminished in the presence of ERK1/2 inhibitor U0126. In conclusion, apoE elicits isoform-dependent effects on macrophage TNF-alpha and IL-6 expression as well as secretion. The ERK1/2 signaling pathways are involved in mediating such apoE isoform-dependent effects.

Sex steroids, APOE genotype and the innate immune system

Microglia are a primary cellular component of the CNS innate immune system. Their response to conserved pathogen motifs is inherent and leads to the release of cytoactive factors that impact surrounding neurons and glia. The microglial response is modified by the local tissue environment and by "global" factors such as gender. Exposure to estrogen and testosterone, in general, down regulate microglia and peripheral macrophage function, promoting an anti-inflammatory phenotype. Other global factors, however, can "override" the gender-based effects demonstrated by estrogen or testosterone. Apolipoprotein E (APOE) genotype and the expression of specific isoforms of apolipoprotein E differentially regulate microglial and peripheral macrophage function. Our studies have shown that the presence of the APOE4 gene, a known risk factor for AD and other neurodegenerative diseases, promotes a pro-inflammatory macrophage phenotype in neonatal microglia. However, in adult mice, the APOE genotype-specific effect depends on gender. Peritoneal macrophages from female adult APOE3 and APOE4 targeted replacement mice do not demonstrate an APOE genotype-specific response, whereas adult male APOE4 targeted replacement mice show enhanced macrophage responsiveness compared to adult male APOE3 mice. At least part of the altered macrophage response in APOE4 male mice may be due to differences in androgen receptor sensitivity to testosterone. These data re-enforce the concept that classical activation in macrophages has multiple levels of regulation, dictated by competing or synergistic factors and genotype.

Effect of apoE/ATP-containing liposomes on hepatic energy state

BACKGROUND/AIMS

ATP-containing liposomes partially prevent ATP depletion in the cold-stored liver. As hepatocytes can specifically bind apoE, we investigated whether the addition of apoE to large (200 nm) ATP-containing liposomes increases their uptake by the liver and further improves hepatic energy stores.

METHODS

Livers from fasted male Hartley guinea-pigs (231 +/- 3 g) were perfused for 90 min under our standard conditions (Control, n = 6) or after a single bolus addition of plain liposomes (Lip, n = 6), ATP (5 micromol)-containing liposomes (ATP-Lip, n = 6) or apoE/ATP-containing liposomes (0.8 or 8mg apoE/g phospholipids; apoE1-Lip and apoE10-Lip, respectively, n = 6 in each group). Liposome uptake and its impact on energy and nitrogen metabolism were studied.

RESULTS

At its highest concentration, apoE significantly increased liposome uptake (apoE10-Lip: - 9.17 +/- 0.69 vs apoE1-Lip: - 6.18 +/- 0.44 vs ATP-Lip: - 6.40 +/- 0.88 nmol min(-1) g(-1) P < 0.05). This was associated with a significant increase in intrahepatic ATP (apoE10-Lip: 1033 +/- 137 vs apoE1-Lip: 811 +/- 98 and ATP-Lip: 648 +/- 36 nmol g(-1); P < 0.05), which was restored to its level in non-perfused livers. Hepatic viability and nitrogen metabolism were not affected.

CONCLUSIONS

Hepatic ATP content being a key factor in the maintenance of liver graft function, apoE/ATP-containing liposomes should be useful in liver preservation for transplantation.

Zebrafish early macrophages colonize cephalic mesenchyme and developing brain, retina, and epidermis through a M-CSF receptor-dependent invasive process

The origin of resident (noninflammatory) macrophages in vertebrate tissues is still poorly understood. In the zebrafish embryo, we recently described a specific lineage of early macrophages that differentiate in the yolk sac before the onset of blood circulation. We now show that these early macrophages spread in the whole cephalic mesenchyme, and from there invade epithelial tissues: epidermis, retina, and brain--especially the optic tectum. In the panther mutant, which lacks a functional fms (M-CSF receptor) gene, early macrophages differentiate and behave apparently normally in the yolk sac, but then fail to invade embryonic tissues. Our video recordings then document for the first time the behavior of macrophages in the invaded tissues, revealing the striking propensity of early macrophages in epidermis and brain to wander restlessly among epithelial cells. This unexpected behavior suggests that tissue macrophages may be constantly "patrolling" for immune and possibly also developmental and trophic surveillance. At 60 h post-fertilization, all macrophages in the brain and retina undergo a specific phenotypic transformation, into "early (amoeboid) microglia": they become more highly endocytic, they down-regulate the L-plastin gene, and abruptly start expressing high levels of apolipoprotein E, a well-known neurotrophic lipid carrier.

Duplicated downstream enhancers control expression of the human apolipoprotein E gene in macrophages and adipose tissue

Two distal enhancers that specify apolipoprotein (apo) E gene expression in isolated macrophages and adipose tissue were identified in transgenic mice that were generated with constructs of the human apoE/C-I/C-I'/C-IV/C-II gene cluster. One of these enhancers, multienhancer 1, consists of a 620-nucleotide sequence located 3.3 kilobases (kb) downstream of the apoE gene. The second enhancer, multienhancer 2, is a 619-nucleotide sequence located 15.9 kb downstream of the apoE gene and 5.9 kb downstream of the apoC-I gene. The two enhancers are 95% identical in sequence, and they are likely to have arisen as a consequence of the gene duplication event that yielded the apoC-I gene and the apoC-I' pseudogene. Both enhancer sequences appear to have equivalent activity in directing apoE gene expression in peritoneal macrophages and in adipocytes, suggesting that their activity in specific cell types may be determined by common regulatory elements.

Apolipoprotein E and multiple sclerosis: a biochemical and genetic investigation

Apolipoprotein E (apo E) is postulated to be a major lipid carrier protein in the brain involved in brain development and repair. Multiple sclerosis (MS) is a major demyelinating disease characterized by destruction of myelin and marked alteration of myelin cholesterol and lipid metabolism. We have determined serum and cerebrospinal fluid (CSF) apo E concentrations using an original time-resolved immunofluorometric assay and calculated intrathecal apo E concentration. Apo E concentrations were determined in 13 control subjects and 129 neurological patients: 34 definite MS patients, 25 with Guillain-Barré syndrome (GBS), 32 with amyotrophic lateral sclerosis (ALS) and 38 with other neurological diseases. Seven clinical parameters (sex, age, age at MS onset, duration of the disease, course, clinical status and disability score) were considered in MS patients. Significant (P < 0.01) decrease in CSF apo E was observed in MS, linked to a decrease in intrathecal apo E. The decreased CSF apo E concentration in MS patients occur independent of the apo E genotype. Apo E is considered as a neurotrophic factor in the brain. Any decrease in intrathecal apo E synthesis would thus contribute to progression of neurological diseases, such as MS.

Microglia, scavenger receptors, and the pathogenesis of Alzheimer's disease

The senile plaque is the pathological hallmark of Alzheimer's disease. Senile plaques are composed of beta amyloid fibrils, associated with activated microglia, astrocytes, and dystrophic neurons. We have recently identified class A scavenger receptors as the main receptors mediating the interaction of microglia with beta amyloid fibrils. Adhesion of microglia to beta amyloid fibrils leads to immobilization of these cells on the fibrils, and induces them to produce reactive oxygen species. We propose that interactions of microglial scavenger receptors with fibrillar beta amyloid may stimulate the microglia to secrete apolipoprotein E and complement proteins, which may further contribute to neurotoxicity and neuronal degeneration. Therefore, microglial scavenger receptors may be novel targets for therapeutic interventions in Alzheimer's disease.

High prevalence of serum apolipoprotein E4 isoprotein in rheumatoid arthritis patients with amyloidosis

OBJECTIVE

To determine whether serum Apolipoprotein E (Apo E) type 4 isoprotein is a risk factor for the development of amyloidosis in patients with rheumatoid arthritis (RA).

METHODS

Using isoelectric focusing, we studied Apo E phenotype expression and the corresponding allele frequencies (epsilon 2, epsilon 3, and epsilon 4) in 35 patients with RA and amyloidosis, 65 patients with RA and without amyloidosis, and 63 healthy controls.

RESULTS

The Apo E3/4 phenotype was significantly more common in the group with amyloidosis (31.4%) than in the patients without amyloidosis (12.3%; P < 0.05) or in healthy controls (12.7%; P < 0.05). The frequency of the epsilon 4 allele was significantly greater in the group with amyloidosis (0.16) than in the patients without amyloidosis (0.07; P < 0.05) or in healthy controls (0.07; P < 0.05).

CONCLUSION

The presence of Apo E4 isoprotein may be a risk factor for the development of amyloidosis in patients with RA.

Functional characterization of two different Kupffer cell populations of normal rat liver

BACKGROUND

Kupffer cells of the liver represent the largest population of tissue macrophages. Small and large Kupffer cells were distinguished in normal liver, leading to the suggestion that they have different functions. This study intends to further characterize small and large Kupffer cells of normal rat liver in vivo and in vitro.

METHODS

Sections of rat liver were investigated by double-staining immunofluorescence with the monoclonal antibodies ED1 and ED2. Isolated nonparenchymal liver cells were separated according to size to obtain small and large Kupffer cells. In culture, phagocytosis was studied by zymosan ingestion and cell proliferation by incorporation of 3H-thymidine. Synthesis of the proteins C1-inhibitor, apolipoprotein E and interleukin-1 was studied by endogenous labeling of newly synthesized proteins, immunoprecipitation and sodium dodecylsulfate-polyacrylamide gel electrophoresis.

RESULTS

ED1+ ED2+ Kupffer cells were located in the liver along the sinusoids. ED1+ ED2+ cells were found mainly located around the central vein and portal vessels. By counterflow elution, small ED1+ ED2- cells were separated from larger ED1+ ED2+ cells and cultured. The larger cells abundantly synthesized C1-inhibitor and apolipoprotein E, while the small cells synthesized only trace amounts of these proteins. Interferon-gamma increased C1-inhibitor synthesis in small (5-fold) and large cells (1.5-fold). 3H-thymidine incorporation was 11-fold higher in small than in large cells. However, lipopolysaccharide-induced pro-interleukin-1 alpha and pro-interleukin-1 beta synthesis and phagocytic activity were similar in both populations.

CONCLUSIONS

The data demonstrate two different populations of mononuclear phagocytes in normal rat liver well distinguished by immunocytochemical and functional markers.

Characterization of an upstream regulatory sequence and its binding protein in the mouse apolipoprotein E gene

The mouse apolipoprotein (apo) E gene from strain C57BL/6 was isolated from a genomic DNA library and its complete nucleotide sequence, together with 1.3 kilobase of 5' flanking DNA and 300 base pairs of the 3' flanking DNA, was determined. Regulatory sequences in the proximal 5' flanking region of the gene were identified. Using a chloramphenicol acetyltransferase transient assay system, positive and negative cis-acting sequences were mapped within 380 base pairs of the 5' flanking region of the mouse apoE gene. Two nuclear protein binding sites were identified within this region by DNase I footprinting. We have characterized one of these regions, termed mouse apoE regulatory sequence (MARS-2), which spans nucleotides -151 to -133. Gel mobility shift assays using oligonucleotides of the MARS-2 sequence having specific deletions or substitutions as probes or competitors showed that the essential sequence of MARS-2 required for nuclear protein binding consists of 16 nucleotides encompassing -151 to -136. When nuclear extracts from different cells were examined, L cells and mouse liver nuclear protein contained the highest levels of binding protein for the MARS-2 probe. This protein, termed MARS-2 binding protein, was purified from mouse liver nuclear extracts to homogeneity using gel filtration and MARS-2 oligonucleotide-specific column chromatographic procedures. The Mr = 66,000 binding protein showed a gel mobility shift band that was identical to that of crude nuclear extracts.

Serum low density lipoprotein of alcoholic patients is chemically modified in vivo and induces apolipoprotein E synthesis by macrophages

This work was carried out to investigate the effect of alcohol drinking on serum LDL. Agarose gel electrophoresis showed that LDL samples from alcoholic patients without serious liver disease were more negatively charged and moved faster toward the cathode than LDL from nondrinking control subjects. Rabbit antibodies raised by using keyhole limpet hemocyanin modified in vitro by 4-hydroxynonenal or by acetaldehyde as immunogens reacted more strongly with patients' LDL than with control LDL, indicating the presence of oxidatively modified epitopes and acetaldehyde adducts in alcoholic patients' LDL. LDL of alcoholic patients has decreased vitamin E contents. The electromobility of LDL decreased after abstinence from alcohol and returned to normal in 2 wk, but this was not accompanied by a significant increase in its vitamin E contents. When incubated with mouse peritoneal macrophages, patients' LDL induced apolipoprotein E secretion by threefold over control LDL with a concomitant increase in cellular cholesterol. Our results thus demonstrate that LDL of alcoholic patients has lower vitamin E content, is chemically modified in vivo, and exhibits altered biological function. These changes in heavy alcoholic drinkers may render LDL more atherogenic and thereby may counter the antiatherosclerosis effects of moderate alcohol consumption.

Oxidative-modified and acetylated low-density lipoproteins differ in their effects on cholesterol synthesis and stimulate synthesis of apolipoprotein E in rat peritoneal macrophages by different mechanisms

Apolipoprotein (apo) E plays an important role in the recognition of lipoproteins by cellular lipoprotein receptors. Unlike other apolipoproteins, apo E is expressed by many extrahepatic tissues including macrophages (M phi). Resident M phi express low levels of apo E. However, their synthesis of apo E is substantially increased after M phi have been incubated with acetylated low-density lipoprotein (LDL). But acetylation of LDL is not known to occur in vivo. On the other hand, modification of LDL by oxidation and by enzymatic action is believed to happen physiologically. In this report, we compared the effects of various modified LDLs on the synthesis of apo E by M phi. Freshly isolated human LDL was modified by (1) repeated addition of acetic anhydride (Ac-LDL); (2) incubation with 20 mumol/L CuSO4 at 37 degrees C for 24 hours (Ox-LDL); and (3) incubation with phospholipase C at 37 degrees C for 1 hour (PI-LDL). Resident peritoneal M phi were collected by lavage from rats and allowed to attach to plastic culture dishes. Although native LDL had no effect, treatment with Ac-, Ox-, and PI-LDL (50 micrograms/mL each) was found to increase medium apo E by (-fold) 4.19 +/- 0.26, 4.20 +/- 0.34, and 2.02 +/- 0.20 (mean +/- SEM, n = 5), respectively, as compared with untreated cells. Northern blot analysis revealed that cellular apo E mRNA was increased in parallel to apo E protein by Ac-LDL and PI-LDL. However, increases of apo E protein and mRNA by Ox-LDL were not equal.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin and cytokines increase hepatic messenger RNA levels and serum concentrations of apolipoprotein J (clusterin) in Syrian hamsters

Infection and inflammation induce alterations in hepatic synthesis and plasma concentrations of the acute phase proteins. Our results show that apolipoprotein (apo) J is a positive acute phase protein. Endotoxin (LPS), tumor necrosis factor (TNF), and interleukin (IL)-1 increased hepatic mRNA and serum protein levels of apo J in Syrian hamsters. Hepatic apo J mRNA levels increased 10- to 15-fold with doses of LPS from 0.1 to 100 micrograms/100 g body weight within 4 h and were elevated for > or = 24 h. Serum apo J concentrations were significantly increased by 16 h and further elevated to 3.3 times that of control, 24 h after LPS administration. Serum apo J was associated with high density lipoprotein and increased fivefold in this fraction, after LPS administration. Hepatic apo J mRNA levels increased 3.5- and 4.6-fold, with TNF and IL-1, respectively, and 8.2-fold with a combination of TNF and IL-1. Serum apo J concentrations were increased 2.3-fold by TNF, 79% by IL-1, and 2.9-fold with a combination of TNF and IL-1. These results demonstrate that apo J is a positive acute phase protein.

Murine macrophages secrete factors that enhance uptake of non-lipoprotein [3H]cholesteryl ester by aortic smooth muscle cells

We have recently demonstrated that macrophage conditioned medium (MP medium) and beta VLDL enhance cholesterol esterification in cultured aortic smooth muscle cells by LDL receptor mediated and other pathways (Stein, O. et al. (1993) Arteroscl. Thromb. 13, 1350-1358). In view of the presence of extracellular non-lipoprotein cholesteryl ester (in the form of lipid droplets) in the atheroma, the effect of MP medium on the cellular uptake of liposomal cholesteryl linoleyl ether (CLE) or cholesteryl ester (CE) was studied. After 4 h incubation in MP medium, the uptake of liposomal [3H]CLE was up to 10-fold higher than in the presence of control medium of the same composition but not conditioned with macrophages (DV medium). Similar results were seen also with HSF derived from LDL receptor negative donors. The MP medium-stimulated uptake of liposomal [3H]CE resulted also in hydrolysis of 70-90% of the labeled compound, indicating that the [3H]CE was intracellular. While the MP medium effect on liposomal [3H]CLE uptake was evident after 4 h, its effect on [3H]cholesterol esterification by SMC in the presence of beta VLDL could be demonstrated only after 24 h. Addition of apoE to MP medium resulted in a small (30-40%) increase in the uptake of liposomal [3H]CLE; however, it was augmented more than 4-fold when apoE was added to DV medium. The MP medium effect on the uptake of liposomal [3H]CLE was interfered with by heparin, anti-LPL antibody or heparinase, while these treatments did not affect [3H]cholesterol esterification in the presence of beta VLDL. These results suggest that the interaction between SMC and two potential sources of lipids in atheroma, i.e., lipoproteins and non-lipoprotein lipid droplets, could be governed by different components of the MP medium. In the case of the lipid droplets, as modeled here in the form of liposomes, macrophage-derived lipoprotein lipase could play a major role in cholesteryl ester transfer into SMC.

Exogenous glucocorticoids increase macrophage secretion of apo E by cholesterol-independent pathways

Macrophage apo E synthesis and secretion has been previously demonstrated to be regulated by intracellular free cholesterol levels and is decreased by cytokines and other inflammatory stimuli associated with macrophage activation. In a recent study, the opposing effects of TGF beta and GM-CSF were reported with the former increasing and the latter decreasing apo E secretion and apo E mRNA levels. In an attempt to further understand the mechanisms by which TGF beta increased apo E expression in mouse peritoneal macrophages, the present study was performed to determine whether pharmacological agents could up-regulate apo E secretion by a mechanism independent of intracellular free cholesterol levels. Agents which resulted in increased apo E secretion were subdivided based on their effects on cAMP elevation. In addition to TGF beta, dexamethasone resulted in significant increases in apo E secretion. The 2-4-fold enhancement in apo E secretion by both TGF beta and dexamethasone occurred without concomitant changes in intracellular cAMP or free cholesterol. Other agents which increased apo E secretion included cholera toxin and 8-bromo-cAMP. While these agents did not affect intracellular cholesterol levels, cholera toxin did increase macrophage cAMP. The changes in apo E secretion by dexamethasone and 8-bromo-cAMP were associated with elevations in apo E mRNA. Dexamethasone-treated macrophages had 6-fold increases in apo E mRNA by 48 h when compared with control macrophages. Macrophages stimulated with 8-bromo-cAMP for 48 h demonstrated a more modest but statistically significant (P < 0.001) 2.2-fold increase. Similar effects of dexamethasone, cholera toxin, TGF beta, and 8-bromo-cAMP on apo E secretion were also apparent in macrophage-derived foam cells. In addition to increasing apo E secretion in macrophages and foam cells, dexamethasone and 8-bromo-cAMP inhibited the down-regulation of apo E secretion mediated by LPS and GM-CSF. Finally, the increased apo E secretion by exogenous glucocorticoids or TGF beta was not species specific as similar effects were observed in rabbit peritoneal macrophages. Therefore, while macrophage activation results in decreased apo E synthesis, macrophages exposed to anti-inflammatory agents including dexamethasone, TGF beta, or following cAMP elevation demonstrate increased apo E secretion by a cholesterol-independent mechanism.

Macrophage-conditioned medium and beta-VLDLs enhance cholesterol esterification in SMCs and HSFs by LDL receptor-mediated and other pathways

Thioglycolate-elicited mouse peritoneal macrophages were incubated for 24 hours in serum-free Dulbecco-Vogt medium containing 0.5% fatty acid-poor bovine serum albumin. This conditioned medium, designated MP medium, was used for experiments with bovine aortic smooth muscle cells (SMCs) or human skin fibroblasts (HSFs). Dulbecco-Vogt medium of the same albumin content but without macrophages served as a control medium. In SMCs labeled from plating the [3H]cholesterol and incubated with hypercholesterolemic rabbit beta-very-low-density lipoprotein (beta-VLDL) in Dulbecco-Vogt medium for 24 hours, there was an increase in cellular [3H]cholesteryl ester (CE) content compared with cells incubated without lipoprotein. When MP medium was used for the incubation of SMCs with beta-VLDL, cellular [3H]cholesteryl ester content increased threefold compared with cells incubated with Dulbecco-Vogt medium. A smaller increase in cholesterol esterification in the presence of MP medium was also encountered with low-density lipoprotein (LDL). The MP medium-induced increase in [3H]cholesterol esterification was not evident up to 6 hours of incubation. Similar results were also obtained with HSFs. The increase in [3H]cholesterol esterification with MP medium in the presence of beta-VLDL was also elicited in cells obtained from LDL receptor-negative donors with familial hypercholesterolemia (FH-HSF), even though in these cells significantly less [3H]cholesteryl ester was formed in the presence of beta-VLDL. MP medium contains numerous agents that could be responsible for the increase in cellular [3H]cholesteryl ester induced by lipoproteins. The first considered was lipoprotein lipase, but lack of inhibition of the MP medium effect by antiserum to lipoprotein lipase did not support this possibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma inhibits macrophage apolipoprotein E production by posttranslational mechanisms

Macrophage-derived apolipoprotein (apo) E and multimers of a synthetic apo E-peptide display monokine-like functions by inhibiting mitogen- or antigen-driven lymphocyte proliferation. This study demonstrated how the target lymphocyte itself can modulate macrophage apo E production. The lymphokine interferon-gamma (IFN) dramatically inhibited the accumulation of apo E in the supernatant of human monocytic THP-1 cells when present during phorbol myristate acetate-induced differentiation. A similar effect was observed when IFN was added to differentiated THP-1 cells. Treatment with IFN did not change the steady-state levels of apo E mRNA. Furthermore, in the presence of IFN no increased degradation or increased uptake of extracellular apo E was detected. Pulse-chase experiments indicated that IFN reduced the accumulation of extracellular apo E and increased the degradation of intracellular apo E. The inhibitory effect of IFN on apo E production also was observed in human monocyte-derived macrophages. Thus, our data demonstrated that IFN inhibited macrophage apo E production by posttranslational mechanisms. This represents a previously uncharacterized immunoregulatory interaction and lends further support to a relationship between lipid metabolism and the immune system.

Cytokine regulation of macrophage apo E secretion: opposing effects of GM-CSF and TGF-beta

Biosynthesis of apolipoprotein (apo) E has been previously demonstrated to be regulated in macrophages by intracellular free cholesterol levels as well as by macrophage activating factors. In this report, the regulation of apo E secretion by cytokines detected within atherosclerotic lesions has been investigated. Granulocyte macrophage-colony stimulating factor (GM-CSF) stimulated macrophages had a 3-5-fold reduction in apo E secretion, comparable to that observed for gamma interferon (IFN gamma), while tumor necrosis factor alpha (TNF alpha) and interleukin 1 beta (IL-1 beta) resulted in a 2-fold decrease. In contrast to the reduction in apo E secretion by these cytokines, transforming growth factor beta (TGF-beta) stimulated macrophages secreted 3-fold greater amounts of apo E than controls. The reduced secretion of apo E by GM-CSF was reversible, heat labile, dose dependent, maximal 48 h after cytokine exposure and was coincident with an increase in fibronectin secretion. The opposing effects of GM-CSF and TGF-beta on apo E secretion were consistent with similar changes detected in apo E mRNA levels. Cytokine effects on apo E secretion in cholesterol loaded macrophages were also investigated and found to be similar to the non-loaded cells with GM-CSF decreasing and TGF-beta increasing apo E secretion. The observed differences in apo E secretion did not correlate with any significant changes in either cellular cholesterol distribution in the non-cholesterol loaded macrophages or in basal ACAT activity. In addition to changes in apo E secretion, cytokine treated macrophages pulsed with [14C]oleate and acetylated LDL for 2-6 h had a 2-fold increase (GM-CSF) or decrease (TGF-beta) in cholesterol esterification. Therefore, GM-CSF and TGF-beta mediated changes in apo E secretion may occur through a mechanism independent of changes in cellular free cholesterol levels. These results suggest that cytokines expressed within an atheroma may play an important role in the modulation of macrophage mediated reverse cholesterol transport.

The acute inflammatory response to lipopolysaccharide in CNS parenchyma differs from that in other body tissues

Acute inflammation is important for defence against infection, wound repair and the mediation of auto-immune tissue destruction. Myelomonocytic recruitment in acute inflammation is a stereotyped and non-specific response to tissue insult which begins within 2 h. In this study, lipopolysaccharide was injected into the murine CNS and other body sites of mice to compare the inflammatory responses. Doses of lipopolysaccharide which induced typical myelomonocytic recruitment in skin and the choroid plexus had no effect in CNS parenchyma, apart from the morphological activation of local resident microglia. The CNS parenchymal response proceeded independently of that in the choroid plexus-cerebral ventricles and had three distinct and unique phases. Initially there was minimal neutrophil exudation and a two-day delay before any increase in macrophage-microglial cell number. Next, there was a rapid increase in macrophage-microglial cell numbers during the third day, mainly due to recruitment of blood monocytes. During this phase, leukocyte recruitment was restricted to monocytes which rapidly adopted the arborized microglial phenotype. Monocytes migrated through an intact blood-brain barrier independent of changes in solute permeability. Finally, there was a florid myelomonocytic reaction predominantly in the white matter, one week after intracerebral injection of 2 micrograms lipopolysaccharide. At this time, the leukocyte reaction disrupted the blood-brain barrier, mononuclear phagocytes expressed macrophage morphology and abundant major histocompatibility complex Class II antigen, and T lymphocytes were present. Myelomonocytic entry into the CNS was partially inhibited by prior blockade of the type 3 complement receptor, known to mediate leukocyte adhesion to endothelium elsewhere. The processes which lead to rapid myelomonocytic recruitment in other tissues are absent in CNS parenchyma. Understanding the molecular mechanisms responsible could have considerable significance both for CNS pathophysiology as well as possible anti-inflammatory therapeutic application elsewhere in the body.

Foam cells from aorta and spleen overexpress apolipoprotein E in the absence of hypercholesterolemia

We have studied Apo E expression in atherosclerotic lesions and spleens in rabbits after a cholesterol-rich diet is discontinued and plasma cholesterol levels return to normal values. After 16 weeks, foam cells are still present in the atherosclerotic lesions and Apo E expression persists restricted solely to the lesion as ascertained by in situ RNA hybridization and northern blot. Apo E expression is induced in spleens of hypercholesterolemic rabbits. However Apo E mRNA levels decrease in this organ parallel to the disappearance of lipid loaded macrophages. These results of in vivo studies indicate that Apo E overexpression in foam cells does not depend on high serum cholesterol levels, but is a characteristic of macrophages that have acquired the foam cell phenotype.

Role of enzyme receptors and inhibitors in regulating proteolytic activities of macrophages

Expression of proteases by neutrophils and other cells with a prominent regulated secretory pathway is determined largely by stimulus-response secretion of proteins prepackaged in high concentration. The regulated secretory pathway is apparently minor in macrophages, and instead proteases are either channeled into lysosomes or secreted constitutively. Posttranslational regulation of macrophage proteases then depends on compartmentalizing enzymes to their sites of primary function. Available data suggest that cells use both specific receptors and inhibitors to accomplish this. Viewed in this context protease inhibitors primarily function to inhibit enzyme not bound to their receptor. Consonant with this model of regulation, connective tissue turnover by macrophages is a contact-dependent process relatively resistant to exogenous macromolecular inhibitors. Although limited information is available regarding determinants that modulate matrix metabolism by human macrophages, this model suggests that determinants of adhesion and colocalization of enzyme and substrate would be as or more important than alterations of inhibitors in the microenvironment of the cell.

Macrophages from nephrotic rats regulate apolipoprotein E biosynthesis and cholesterol content independently

The effects of the nephrotic syndrome in rats on the cholesterol content and the biosynthesis of apolipoprotein E (apoE) by resident peritoneal macrophages have been investigated. Since the nephrotic syndrome has been associated with an increased risk of coronary atherosclerosis, we hypothesized that macrophages from nephrotic rats would accumulate cholesterol and undergo transformation into foam cells, with a concomitant increase in apoE biosynthesis. The nephrotic syndrome was induced in rats with puromycin aminonucleoside. Peritoneal macrophages exposed in vivo for 7-21 d to ascites fluid derived from plasma containing sixfold elevations of lipoproteins did not accumulate unesterified or esterified cholesterol. Nevertheless, immunoprecipitation assays after incubation of the isolated cells with [35S]methionine, or immunoblot analysis of the incubation medium demonstrated a 2.6-fold increase in apoE secretion compared with normal macrophages. This increase was accompanied by 5- to 10-fold increases in cellular apoE messenger RNA as determined by quantitative solution hybridization assay. Peritoneal macrophages cultured from nephrotic rats during the period of hypercholesterolemia also showed distinct and highly reproducible morphologic changes. The dissociation between apoE biosynthesis and macrophage cholesterol content provides new insight into the response of peritoneal macrophages in vivo to endogenous hyperlipemia.

Apolipoprotein E expression by human-monocyte-derived macrophages. Modulation by opsonised zymosan and cholesterol

The effects of opsonised zymosan and of acetylated low-density lipoprotein (AcLDL) on the synthesis and secretion of apolipoprotein E (apoE), and of apoE mRNA abundance, have been studied in human-monocyte-derived macrophages (MDM). Stimulation by opsonised zymosan led to a concentration-dependent increase in apoE secretion; non-opsonised zymosan was without effect. Incubation with AcLDL led to a concentration-dependent elevation in apoE synthesis which paralleled the increase in cellular cholesterol content. The opsonised-zymosan-induced stimulation of apoE production was additive to that resulting from cholesterol loading with AcLDL. Opsonised zymosan alone did not affect the cholesterol content of MDM. Cholesterol-loaded MDM remained responsive to opsonised zymosan stimulation, displaying a 3.5-fold elevation in apoE secretion as compared to their non-stimulated counterparts. Cell-associated apoE remained at trace levels under all conditions of cell treatment. Studies involving [35S]methionine incorporation showed de novo synthesis of apoE to be enhanced in both cholesterol-loaded and opsonised-zymosan-stimulated macrophages. Estimation of apoE mRNA in opsonised-zymosan-stimulated and control MDM by dot-blot analysis revealed similar message abundance; by contrast, elevation in cellular cholesterol content following incubation with modified LDL led to a significant increase in apoE mRNA levels. We conclude that the opsonised-zymosan-induced stimulation of apoE synthesis and secretion in human MDM may occur by a mechanism(s) independent of cellular cholesterol content.

Effects of activation on lipid and lipoprotein metabolism in murine macrophages

The effects of activation on lipid and lipoprotein metabolism were examined in resident murine macrophages, inflammatory cells elicited by thioglycolate, primed cells elicited by pyran copolymer, and activated cells elicited by Corynebacterium parvum. Low density lipoprotein receptors were reduced by 70%, while scavenger receptors were reduced 60% in activated cells. Basal cholesteryl ester and triglyceride synthesis were increased fourfold in activated cells, whereas the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase was high in resident cells and progressively declined by greater than 80% in activated cells. Activities of neutral cholesteryl esterase and neutral triglyceride lipase were increased two- to fourfold in inflammatory, primed, and activated macrophages. These results demonstrate the diverse changes in lipid and lipoprotein metabolism that occur with activation and emphasize how the behavior of macrophages in atherosclerotic lesions can be altered by activation.

Sulfation of rat apolipoprotein E

The synthesis of a 37-kilodalton (kDa) protein which has been shown recently to be identical with apolipoprotein E (apo-E) was increased after sciatic nerve injury of the rat. When regeneration of the nerve was allowed, its synthesis returned to control levels at about 8 weeks post injury. In this report it is shown that similar time-course studies of the protein in the rat optic nerve revealed a delayed increase of the protein but a comparably high level of synthesis at 3 weeks post injury. This level was maintained up to at least 18 weeks after crush. Furthermore, two-dimensional electrophoresis revealed that the characteristic "trailing" of the protein is due to its sialylation, because it was reduced after neuraminidase treatment. This treatment, however, detected a neuraminidase-resistant heterogeneous form in CNS tissue and a homogeneous form in peripheral nervous tissue. The trailing persisted up to 18 days of culture of optic nerve explants, of CNS glial cells, and of peritoneal macrophages, but disappeared during the first culture days of sciatic nerve explants and was not observed in Schwann cell culture media. Incorporation studies with 35SO4 revealed that apo-E was the major sulfated protein in culture media conditioned by CNS glial cells, whereas sulfation of the protein was undetectable in Schwann cell cultures. Because macrophages are likely to be the major source of apo-E in both peripheral and central glial cell cultures as well as in injured optic and sciatic nerves, it is hypothesized that resident cells of sciatic nerves secrete potent sulfatases. As a result, sialic acid residues may be more susceptible to degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Fat-storing (Ito) cells of rat liver synthesize and secrete apolipoproteins: comparison with hepatocytes

Fat-storing cells of the liver store most of the vitamin A of the body. Vitamin A is present in a few large fat droplets within the cell. The aim of our study was to investigate apolipoprotein biosynthesis in isolated fat-storing cells from rat liver during the time in culture. Isolated rat hepatocytes were studied for comparison. Proteins were biosynthetically labeled and further identified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Apoproteins in culture supernatants were identified by density gradient ultracentrifugation and by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of aliquots of the gradient. Rat plasma was processed in the same way and used for comparison. Fat-storing cells synthesized and secreted apoprotein E, apoprotein A-I, apoprotein A-IV, and low amounts of apoprotein C. The synthesis of these proteins increased during the culture time, reaching a maximum at the fifth day after isolation. The proteins were identified mostly as apoproteins of high-density lipoprotein. Hepatocytes synthesized and secreted apoproteins of all classes of lipoproteins. The distribution of high-density lipoprotein apoproteins was similar to that of fat-storing cells but hepatocytes produced larger amounts of the apoproteins.

A role for apolipoprotein E, apolipoprotein A-I, and low density lipoprotein receptors in cholesterol transport during regeneration and remyelination of the rat sciatic nerve

Recent work has demonstrated that apo E secretion and accumulation increase in the regenerating peripheral nerve. The fact that apoE, in conjunction with apoA-I and LDL receptors, participates in a well-established lipid transfer system raised the possibility that apoE is also involved in lipid transport in the injured nerve. In the present study of the crushed rat sciatic nerve, a combination of techniques was used to trace the cellular associations of apoE, apoA-I, and the LDL receptor during nerve repair and to determine the distribution of lipid at each stage. After a crush injury, as axons died and Schwann cells reabsorbed myelin, resident and monocyte-derived macrophages produced large quantities of apoE distal to the injury site. As axons regenerated in the first week, their tips contained a high concentration of LDL receptors. After axon regeneration, apoE and apoA-I began to accumulate distal to the injury site and macrophages became increasingly cholesterol-loaded. As remyelination began in the second and third weeks after injury, Schwann cells exhausted their cholesterol stores, then displayed increased LDL receptors. Depletion of macrophage cholesterol stores followed over the next several weeks. During this stage of regeneration, apoE and apoA-I were present in the extracellular matrix as components of cholesterol-rich lipoproteins. Our results demonstrate that the regenerating peripheral nerve possesses the components of a cholesterol transfer mechanism, and the sequence of events suggests that this mechanism supplies the cholesterol required for rapid membrane biogenesis during axon regeneration and remyelination.

Directed exocytosis of secretory granules containing apolipoprotein E to the adherent surface and basal vacuoles of macrophages spreading on immobile immune complexes

As macrophages spread on an immune complex-coated surface, large, clear basal vacuoles and numerous coated vesicles and tubules form rapidly and are occasionally contiguous with the adherent surface, creating a microcompartment between the immune complex-coated surface and the cell membrane. The present study explored the nature of this basal compartment by examining the distribution of a major secretory product of macrophages, apolipoprotein E (ApoE), and of a lysosomal enzyme, acid phosphatase, by enzyme and immunocytochemistry. Upon contact of the macrophages with the immune complexes, intracellular stores of ApoE were secreted rapidly in the first 10 to 20 minutes to the area of ligand-receptor interaction. ApoE filled the large basal vacuoles and was also found in invaginations on the adherent surface that were sealed to the influx of proteins and peptides from the bulk medium. In contrast, the contents of lysosomes were not redistributed to the basal compartment. By 2 hours most of the ApoE had appeared in the bulk medium, suggesting that the protein could move out of the basal compartment. These data suggest that specific ligand-Fc receptor interactions serve to target secretion by macrophages to selective focal areas of contact, and that there are also mechanisms for retrieval of material from these sites.

Tumor-induced variations in a high molecular weight inhibitory monokine

A soluble inhibitor of T cell proliferation was demonstrated in splenic and peritoneal macrophage (M phi) culture supernatants and was variably glycosylated during tumor development. This factor(s) inhibited mixed lymphocyte reaction- (MLR) and concanavalin A-induced T cell proliferation and was not prostaglandin E2 (PGE2), as demonstrated by size (nondialyzable, found in a 30 kilodalton [kd] ultrafiltration retentate and in fractions corresponding to greater than 67 kd on S-200 Sephacryl chromatography) and time course of activity in the MLR. Concentrated supernatants were PGE2-free and yet inhibited proliferation in the MLR. Isoelectric focusing (IEF) revealed normal and tumor-bearing host (TBH) concentrated M phi supernatants' major peaks of inhibitory activity differed in charge, with a pI of 6.5-7.6 for normal hosts and 4.0-6.0 for TBH. Activity in TBH M phi supernatants was found primarily in fractions eluting from hydroxylapatite at 0.3 M sodium phosphate buffer, pH 7.3, was resistant to proteolytic enzymes, but was sensitive to neuraminidase. In contrast, inhibitory activity in normal host M phi supernatants eluted from hydroxylapatite at 0.6 M sodium phosphate buffer and was not sensitive to neuraminidase. Thus, variable glycosylation (presence and absence of sialic residues) could account for the charge difference seen in IEF and may have a bearing on tumor-induced hyporesponsiveness. Kinetic addition of supernatants to the MLR revealed PGE2 may be required for inhibitory activity to be manifested early (0 and 24 h) but not if the high molecular weight (mw) inhibitor was added late (48 and 72 h post initiation). Both normal and TBH M phi supernatants suppressed the generation of interleukin 2 (IL 2) with a dose- and time-dependent difference. Cell-cycle analysis of mitogen-stimulated cells treated with normal and TBH M phi supernatants revealed that TBH M phi supernatants enhanced cell-cycle progression when measured early, but that both normal and TBH M phi supernatants suppressed the number of cells in S phase when measured late in the assay. The production of a high mw inhibitor by both normal and TBH M phi could suggest a homeostatic mechanism, which was upset by increased PGE2 production and production of an inhibitor containing sialic acid, tipping the balance in favor of immunosuppression.

Novel method for studying mRNA phenotypes in single or small numbers of cells

Biological processes, such as growth control, are often governed by biochemical steps involving mRNA transcripts that are short-lived and have a low copy number. Furthermore, the cells involved in these processes are often available in low numbers from in vivo sources. We now report a method that is superior to in situ hybridization, RNA blot analysis, and the nuclease protection assay for the study of short-lived, low-copy-number mRNA transcripts. The method consists of a microprocedure for isolating RNA from one to a few thousand cells and two coupled enzymatic steps: reverse transcription of whole cellular RNA, followed by amplification of the cDNA by a specifically primed polymerase chain reaction to give specific cDNA fragments that can be visualized on agarose gels by ethidium bromide staining. With this method we have detected actin mRNA from a single cell, or less than 100 cRNA molecules, and have quantified differences in RNA concentrations of less than threefold. The reverse transcription reaction products can be divided for the polymerase chain reaction, and several mRNA species can be assayed simultaneously. Therefore, we call the method single-cell mRNA phenotyping. This technique is applicable to the analysis of low-copy-number growth factor transcripts in cells in culture and in vivo.

Oligodendrocytes but not astrocytes express apolipoprotein E after injury of rat optic nerve

Apolipoprotein E (apoE), a lipid-binding glycoprotein involved in transport and metabolism of phospholipids and cholesterol, is synthesized and secreted at elevated rates following transection of mature rat peripheral and central nerves. In the peripheral nervous system (PNS) infiltrating macrophages express apoE during Wallerian degeneration. Following injury of the optic nerve (ON) apoE synthesis is significantly stimulated but the apoE-expressing cells have thus far not been identified. This study used 1 micron and thin cryosections to identify the cellular source of apoE in transected ON. Serial 1 micron frozen sections were stained by avidin-biotin-peroxidase complex immunocytochemistry by using a specific antiserum to apoE and by antibodies that identify different cell types: glial fibrillary acidic protein (GFAP) for astrocytes, 2',3'-cyclic nucleotide-3' phosphodiesterase (CNP) for oligodendrocytes, and ED1 for macrophages. In normal ON both astrocytes and oligodendrocytes were apoE-positive. One week after ON transection oligodendrocytes accounted for the majority of apoE-positive cells, while apoE immunoreactivity had disappeared from astroglial cell bodies and processes. In contrast to the PNS only a few ED1/apoE-positive macrophages were present in ON 7 days after transection. By using immunogold-labeled ultrathin cryosections apoE could be localized in the Golgi apparatus of oligodendrocytes, indicating synthesis by these cells. Our data suggest that oligodendrocyte-derived apoE protein may participate in the redistribution of myelin lipids after CNS injury.

Biochemical nature and cellular origin of amyloid enhancing factor (AEF) as determined by anti-AEF antibody

Low ionic strength acidic buffer, Sephadex G-200 and Benzamidine-Sepharose (BZ) gel chromatography, have been used for the partial purification of alveolar hydatid cyst (AHC) induced amyloid enhancing factor (AEF). BZ-gel bound AEF (AEF-BZ) demonstrated AEF activity in the mouse bioassay, proteolytic activity against Hide powder azure showed two major and three minor peptides on SDS-PAGE. Pretreatment of AEF-BZ with 10 mM phenylmethylsulphonyl fluoride or 20 mM p-chloromercuribenzoic acid completely abolished its bioactivity in vivo and proteolytic activity in vitro. Polyclonal anti-AEF antibody (AAA) was generated which on passive transfer into mice completely abolished the bioactivity of both casein-induced, or AHC-induced AEF. The AAA absorbed on Sepharose gel conjugated to normal mouse serum developed one common precipitin band between AE and AEF-positive sera from AHC-infected and old retired mice and in immunostaining it bound to the cytoplasmic granular components of a majority of splenic and peritoneal leucocytes from AHC-infected mice. In contrast, only a few normal mouse leucocytes showed positive staining. We suggest that AEF, in all probability, is a serine/thiol protease of leucocyte origin whose intracellular and humoral concentrations increase significantly during amyloidosis. The role of lysosomal proteases and anti-AEF antibody which has been successfully generated for the first time is discussed with reference to the origin of AEF and its presumed biological function in amyloidogenesis.

Wound macrophages express TGF-alpha and other growth factors in vivo: analysis by mRNA phenotyping

The presence of macrophages is required for the regeneration of many cell types during wound healing. Macrophages have been reported to express a wide range of mitogenic factors and cytokines, but none of these factors has been shown in vivo to sustain all the wound-healing processes. It has been suggested that transforming growth factor-alpha (TGF-alpha) may mediate angiogenesis, epidermal regrowth, and formation of granulation tissue in vivo. Macrophages isolated from a wound site, and not exposed to cell culture conditions, expressed messenger RNA transcripts for TGF-alpha, TGF-beta, platelet-derived growth factor A-chain, and insulin-like growth factor-1. The expression of these transcripts was determined by a novel method for RNA analysis in which low numbers of mouse macrophages were isolated from wound cylinders, their RNA was purified and reverse-transcribed, and the complementary DNA was amplified in a polymerase chain reaction primed with growth factor sequence-specific primers. This single-cell RNA phenotyping procedure is rapid and has the potential for quantification, and mRNA transcripts from a single cell or a few cells can be unambiguously demonstrated, with the simultaneous analysis of several mRNA species. Macrophages from wounds expressed TGF-alpha antigen, and wound fluids contained TGF-alpha. Elicited macrophages in culture also expressed TGF-alpha transcripts and polypeptide in a time-dependent manner after stimulation with modified low-density lipoproteins and lipopolysaccharide endotoxin, which are characteristic of the activators found in injured tissues.

Apolipoprotein E: cholesterol transport protein with expanding role in cell biology

Apolipoprotein E is a plasma protein that serves as a ligand for low density lipoprotein receptors and, through its interaction with these receptors, participates in the transport of cholesterol and other lipids among various cells of the body. A mutant form of apolipoprotein E that is defective in binding to low density lipoprotein receptors is associated with familial type III hyperlipoproteinemia, a genetic disorder characterized by elevated plasma cholesterol levels and accelerated coronary artery disease. Apolipoprotein E is synthesized in various organs, including liver, brain, spleen, and kidney, and is present in high concentrations in interstitial fluid, where it appears to participate in cholesterol redistribution from cells with excess cholesterol to those requiring cholesterol. Apolipo-protein E also appears to be involved in the repair response to tissue injury; for example, markedly increased amounts of apolipoprotein E are found at sites of peripheral nerve injury and regeneration. Other functions of apolipoprotein E, unrelated to lipid transport, are becoming known, including immunoregulation and modulation of cell growth and differentiation.

Dyslipoproteinemia in systemic lupus erythematosus. Effect of corticosteroids

The increased incidence of atherosclerotic coronary artery disease in patients with systemic lupus erythematosus (SLE) may be due to a dyslipoproteinemia caused by corticosteroid administration. To determine whether lipoprotein lipid levels are abnormal in SLE and the relation of lipoprotein levels to corticosteroid use, lipid and apolipoprotein levels were measured in 46 female patients with SLE and 30 matched control subjects. The patients with SLE had higher levels of plasma triglyceride (134 versus 73 mg/dl; p less than 0.001), cholesterol (201 versus 168 mg/dl; p less than 0.001), and low-density lipoprotein cholesterol (121 versus 94 mg/dl; p less than 0.001) than control subjects. The levels of high-density lipoprotein cholesterol, high-density lipoprotein subfraction 3 cholesterol, and apolipoprotein Al were similar in the two groups, but high-density lipoprotein subfraction 2 cholesterol was lower in the patients with SLE (10.2 versus 18.2 mg/dl; p less than 0.001). When patients with SLE treated with prednisone (n = 32) were compared to patients with SLE not treated with prednisone (n = 14), the former had higher triglyceride (158 versus 87 mg/dl; p less than 0.001), cholesterol (214 versus 170 mg/dl; p less than 0.001), and low-density lipoprotein cholesterol (130 versus 103 mg/dl; p less than 0.001) levels. The patients with SLE not treated with prednisone had lipid levels similar to those in control subjects except that high-density lipoprotein cholesterol was lower (49.7 versus 59.0 mg/dl; p less than 0.05). The daily prednisone dosage in the treated patients with SLE correlated with levels of cholesterol (r = 0.38, p less than 0.02), high-density lipoprotein cholesterol (r = 0.40, p less than 0.02), and high-density lipoprotein subfraction 3 cholesterol (r = 0.47, p less than 0.01). Thus, female patients with SLE have a dyslipoproteinemia of the type that would place them at an increased risk for coronary artery disease. Corticosteroids, used in the treatment of SLE, seem to play a role in the pathogenesis of the observed lipoprotein abnormalities.