Mouse apolipoprotein J: characterization of a gene implicated in atherosclerosis

The normalizing effects of the CYP46A1 activator efavirenz on retinal sterol levels and risk factors for glaucoma in Apoj-/- mice

Apolipoprotein J (APOJ) is a multifunctional protein with genetic evidence suggesting an association between APOJ polymorphisms and Alzheimer's disease as well as exfoliation glaucoma. Herein we conducted ocular characterizations of Apoj^-/- mice and found that their retinal cholesterol levels were decreased and that this genotype had several risk factors for glaucoma: increased intraocular pressure and cup-to-disk ratio and impaired retinal ganglion cell (RGC) function. The latter was not due to RGC degeneration or activation of retinal Muller cells and microglia/macrophages. There was also a decrease in retinal levels of 24-hydroxycholesterol, a suggested neuroprotectant under glaucomatous conditions and a positive allosteric modulator of N-methyl-D-aspartate receptors mediating the light-evoked response of the RGC. Therefore, Apoj^-/- mice were treated with low-dose efavirenz, an allosteric activator of CYP46A1 which converts cholesterol into 24-hydroxycholesterol. Efavirenz treatment increased retinal cholesterol and 24-hydroxycholesterol levels, normalized intraocular pressure and cup-to-disk ratio, and rescued in part RGC function. Retinal expression of Abcg1 (a cholesterol efflux transporter), Apoa1 (a constituent of lipoprotein particles), and Scarb1 (a lipoprotein particle receptor) was increased in EVF-treated Apoj^-/- mice, indicating increased retinal cholesterol transport on lipoprotein particles. Ocular characterizations of Cyp46a1^-/- mice supported the beneficial efavirenz treatment effects via CYP46A1 activation. The data obtained demonstrate an important APOJ role in retinal cholesterol homeostasis and link this apolipoprotein to the glaucoma risk factors and retinal 24-hydroxycholesterol production by CYP46A1. As the CYP46A1 activator efavirenz is an FDA-approved anti-HIV drug, our studies suggest a new therapeutic approach for treatment of glaucomatous conditions.

Concentration-dependent effects of 17β-estradiol and bisphenol A on lipid deposition, inflammation and antioxidant response in male zebrafish (Danio rerio)

Environmental estrogenic compounds are important pollutants, which are widely distributed in natural water bodies. They produce various adverse effects on fish, but their concentration-dependent toxicities in fish metabolism and health are not fully understood. This study investigated the effects of 17β-estradiol (E2) and bisphenol A (BPA) at low and high concentrations on lipid deposition, inflammation and antioxidant response in male zebrafish. We measured fish growth parameters, gonad development, lipid contents and the activities of inflammatory and antioxidant enzymes, as well as their mRNA expressions. All E2 and BPA concentrations used increased body weight, damaged gonad structure and induced feminization in male zebrafish. The exposure of zebrafish to E2 and BPA promoted lipid accumulation by increasing total fat, liver triglycerides and free fatty acid contents, and also upregulated lipogenic genes expression, although they decreased total cholesterol content. Notably, zebrafish exposed to low concentrations of E2 (200 ng/L) and BPA (100 μg/L) had higher lipid synthesis and deposition compared to high concentrations (2000 ng/L and 2000 μg/L, respectively). However, the high concentrations of E2 and BPA increased inflammation and antioxidant response. Furthermore, BPA caused greater damage to fish gonad development and more severe lipid peroxidation compared to E2. Overall, the results suggest that the toxic effects of E2 and BPA on zebrafish are concentration-dependent such that, the relative low concentrations used induced lipid deposition, whereas the high ones caused adverse effects on inflammation and antioxidant response.

Evaluation of Tear Fluid and Aqueous Humor Concentration of Clusterin as Biomarkers for Early Diagnosis of Pseudoexfoliation Syndrome and Pseudoexfoliative Glaucoma

PURPOSE

Pseudoexfoliation syndrome (PEX) is an age-related disorder of the extracellular matrix characterized by the accumulation of fibrillary deposits in the anterior chamber of the eye, which leads to the development of pseudoexfoliative glaucoma (PEG). Early identification of subjects with higher susceptibility to PEX and PEG development is very important so that these conditions are managed at earlier stages, which requires that an objective biomarker is defined. Therefore, in the present study, we aimed to determine if aqueous humor and tear fluid concentrations of clusterin, an extracellular chaperone, are objective biomarkers for PEX and PEG risk.

METHODS

Tear fluid was obtained from 80 patients with PEG, 80 patients with PEX, and 80 controls, using Schirmer strips. Aqueous humor was also collected during cataract surgery from 12 patients with PEG, 17 patients with PEX, and 22 controls, who also gave tear samples. Clusterin concentration was determined by ELISA.

RESULTS

Clusterin concentration in aqueous humor was significantly higher in patients with PEG than in PEX cases (P = .002) and controls (P = .004). Receiver operating characteristics analysis revealed that this parameter is a robust classifier to distinguish PEG and PEX cases. Tear fluid clusterin concentrations did not differ significantly between groups. Aqueous humor and tear fluid levels of clusterin were not significantly correlated.

CONCLUSIONS

In conclusion, tear fluid clusterin level in patients with PEG and PEX was determined for the first time, which showed no difference between study groups. Aqueous humor clusterin level was markedly higher in patients with PEG.

Brain clusterin protein isoforms and mitochondrial localization

Clusterin (CLU), or apolipoprotein J (ApoJ), is the third most predominant genetic risk factor associated with late-onset Alzheimer’s disease (LOAD). In this study, we use multiple rodent and human brain tissue and neural cell models to demonstrate that CLU is expressed as multiple isoforms that have distinct cellular or subcellular localizations in the brain. Of particular significance, we identify a non-glycosylated 45 kDa CLU isoform (mitoCLU) that is localized to the mitochondrial matrix and expressed in both rodent and human neurons and astrocytes. In addition, we show that rodent mitoCLU is translated from a non-canonical CUG (Leu) start site in Exon 3, a site that coincides with an AUG (Met) in human CLU. Last, we reveal that mitoCLU is present at the gene and protein level in the currently available CLU^–/– mouse model. Collectively, these data provide foundational knowledge that is integral in elucidating the relationship between CLU and the development of LOAD.

High serum clusterin levels are associated with premature coronary artery disease in a Chinese population

BACKGROUND

Clusterin plays an important role in the cardiovascular system, and serum levels of clusterin are higher in coronary artery disease patients. Here, we measured serum clusterin levels in premature coronary artery disease (PCAD) patients and explored the association of these levels with PCAD risk.

METHODS

Serum samples and general clinical information were obtained from 672 subjects including 364 PCAD subjects, 126 non-PCAD subjects, and 182 controls.

RESULTS

Serum clusterin levels were higher in PCAD patients than in controls, particularly in males with body mass index (BMI) < 25 kg/m² (P < 0.0001). Compared with the lowest tertile of clusterin, the odds ratio of PCAD in the highest tertile was higher in both a univariate and three adjustment models, and it was 3.146-fold higher in Model 3. This association was especially significant in subgroups with BMI < 25 kg/m² , total cholesterol < 5.7 mmol/L, high-density lipoprotein cholesterol ≥ 1.0 mmol/L, Urea < 7.14 mmol/L, and estimated glomerular filtration rate < 90 mL/min/1.73 m² . Serum clusterin may be a potential diagnostic biomarker for PCAD (sensitivity 60.7%, specificity 51.6%, area under the curve 0.595 [95% CI, 0.544-0.647], P < 0.0001), and a combination of clusterin with clinical variables in Model 3 resulted in improved diagnostic accuracy (sensitivity 86.3%, specificity 64.2%, area under the curve 0.829 [95% CI, 0.782-0.877], P < 0.0001).

CONCLUSIONS

Serum clusterin levels were increased in PCAD patients, especially for males with BMI < 25 kg/m² . Higher clusterin levels were independently associated with the presence of PCAD, particularly in subjects with normal BMI, lower total cholesterol, urea, estimated glomerular filtration rate, and higher high-density lipoprotein cholesterol. Clusterin might be a potential diagnostic biomarker for PCAD patients, especially in combination with clinical variables.

Genetic variation in clusterin and risk of dementia and ischemic vascular disease in the general population: cohort studies and meta-analyses of 362,338 individuals

BACKGROUND

Clusterin, also known as apolipoprotein J (apoJ), is one of the most abundantly expressed apolipoproteins in the brain after apolipoprotein E (apoE). Like the ε4 allele of the apolipoprotein E gene (APOE), the clusterin gene (CLU) is a risk locus for Alzheimer's disease, and may play additional roles in atherosclerosis pathogenesis. We tested whether genetic variation in CLU was associated with either Alzheimer's disease or atherosclerosis-related diseases.

METHODS

We studied individual data on 103,987 participants from the Copenhagen General Population Study (CGPS) and the Copenhagen City Heart Study (CCHS). We genotyped a common CLU variant (rs9331896) and two common APOE variants (rs7412 and rs429358), defining the ε2, ε3, and ε4, alleles in CGPS and CCHS. All individuals in the CGPS and CCHS cohorts were followed from study inclusion to occurrence of event, death, emigration, or until 10 November 2014, whichever came first. Summary consortia data on 258,351 individuals from the International Genomics of Alzheimer's Project (IGAP) and the Coronary Artery Disease Genome-wide Replication and Meta-analysis plus the Coronary Artery Disease (C4D) Genetics and 1000-Genomes-based genome-wide association studies (CARDIoGRAMplusC4D) were used in meta-analyses.

RESULTS

In CGPS and CCHS, multifactorially adjusted hazard ratios for Alzheimer's disease, all dementia, vascular dementia, ischemic cerebrovascular disease, and ischemic heart disease were 1.18 (1.07-1.30), 1.09 (1.02-1.17), 0.96 (0.80-1.17), 1.02 (0.97-1.07), and 0.97 (0.93-1.01) per T allele, respectively. Multifactorially adjusted hazard ratios for Alzheimer's disease and all dementia were 2.72 (2.45-3.01) and 2.21 (2.05-2.38) for the APOE ɛ4 allele. There was no interaction between rs9331896 in CLU and rs429358 (defining the ɛ4 allele) in APOE in predicting Alzheimer's disease or all dementia (P = 0.39 and P = 0.21). In a meta-analysis including consortium data, the overall fixed- and random-effects odds ratios for Alzheimer's disease per T allele were 1.16 (1.13-1.18) (I 2 = 0.0%; P for heterogeneity = 0.89).

CONCLUSIONS

A common variant in CLU was associated with a high risk of Alzheimer's disease and all dementia in the general population but not with vascular dementia or ischemic vascular disease. Important novel aspects compared to previous studies are the incorporation of individual risk factor data, the exact causative ε4 allele, and several subtypes of dementia and atherosclerosis-related endpoints.

The impact of growth hormone on proteomic profiles: a review of mouse and adult human studies

Growth hormone (GH) is a protein that is known to stimulate postnatal growth, counter regulate insulin's action and induce expression of insulin-like growth factor-1. GH exerts anabolic or catabolic effects depending upon on the targeted tissue. For instance, GH increases skeletal muscle and decreases adipose tissue mass. Our laboratory has spent the past two decades studying these effects, including the effects of GH excess and depletion, on the proteome of several mouse and human tissues. This review first discusses proteomic techniques that are commonly used for these types of studies. We then examine the proteomic differences found in mice with excess circulating GH (bGH mice) or mice with disruption of the GH receptor gene (GHR^-/-). We also describe the effects of increased and decreased GH action on the proteome of adult patients with either acromegaly, GH deficiency or patients after short-term GH treatment. Finally, we explain how these proteomic studies resulted in the discovery of potential biomarkers for GH action, particularly those related with the effects of GH on aging, glucose metabolism and body composition.

Immune-Mediated Inflammation May Contribute to the Pathogenesis of Cardiovascular Disease in Mucopolysaccharidosis Type I

Background

Cardiovascular disease, a progressive manifestation of α-L-iduronidase deficiency or mucopolysaccharidosis type I, continues in patients both untreated and treated with hematopoietic stem cell transplantation or intravenous enzyme replacement. Few studies have examined the effects of α-L-iduronidase deficiency and subsequent glycosaminoglycan storage upon arterial gene expression to understand the pathogenesis of cardiovascular disease.

Methods

Gene expression in carotid artery, ascending, and descending aortas from four non-tolerized, non-enzyme treated 19 month-old mucopolysaccharidosis type I dogs was compared with expression in corresponding vascular segments from three normal, age-matched dogs. Data were analyzed using R and whole genome network correlation analysis, a bias-free method of categorizing expression level and significance into discrete modules. Genes were further categorized based on module-trait relationships. Expression of clusterin, a protein implicated in other etiologies of cardiovascular disease, was assessed in canine and murine mucopolysaccharidosis type I aortas via Western blot and in situ immunohistochemistry.

Results

Gene families with more than two-fold, significant increased expression involved lysosomal function, proteasome function, and immune regulation. Significantly downregulated genes were related to cellular adhesion, cytoskeletal elements, and calcium regulation. Clusterin gene overexpression (9-fold) and protein overexpression (1.3 to 1.62-fold) was confirmed and located specifically in arterial plaques of mucopolysaccharidosis-affected dogs and mice.

Conclusions

Overexpression of lysosomal and proteasomal-related genes are expected responses to cellular stress induced by lysosomal storage in mucopolysaccharidosis type I. Upregulation of immunity-related genes implicates the potential involvement of glycosaminoglycan-induced inflammation in the pathogenesis of mucopolysaccharidosis-related arterial disease, for which clusterin represents a potential biomarker.

Plasma Clusterin and Lipid Profile: A Link with Aging and Cardiovascular Diseases in a Population with a Consistent Number of Centenarians

The role of Clusterin in attenuation of inflammation and reverse cholesterol transfer makes this molecule a potential candidate as a marker for cancer, cardiovascular disease, diabetes mellitus, and metabolic syndrome. In elderly subjects cardiovascular diseases represent the primary cause of death and different clinical studies have shown a positive correlation of these diseases with changes in the lipid pattern. This work aimed at evaluating the relationship between circulating clusterin and the biochemical parameters that characterize the lipid profile of a Sardinian population divided into five age groups including centenarians; the high frequency in Sardinia of these long-lived individuals gave us the opportunity to extend the range of the age groups to be analyzed to older ages and to better evaluate the changes in the lipid balance during ageing and its relationship with clusterin concentration in plasma. Our results showed that Clusterin concentration values of the youngest group were more similar with the centenarian's group compared to the other age groups, and a positive correlation arises with LDL. Furthermore given the high prevalence of cardiovascular diseases in the population examined and the association of Clusterin with these pathologies we evaluated Clusterin concentration variation in two groups with or without cardiovascular diseases. In presence of cardiovascular disease, Clusterin is significantly related to the most atherogenic components of lipid profile (total cholesterol and LDL), especially in women, suggesting its potential role in modulating cardiovascular metabolic risk factors.

Deficiency of clusterin exacerbates high-fat diet-induced insulin resistance in male mice

The present study examined the role of clusterin in insulin resistance in high fat-fed wild-type and clusterin knockout (KO) mice. The plasma levels of glucose and C-peptide and islet size were increased in clusterin KO mice after an 8-week high-fat diet. In an ip glucose tolerance test, the area under the curve for glucose was not different, whereas the area under the curve for insulin was higher in clusterin KO mice. In a hyperinsulinemic-euglycemic clamp, the clamp insulin levels were higher in clusterin KO mice after the high-fat diet. After adjusting for the clamp insulin levels, the glucose infusion rate, suppression of hepatic glucose production, and glucose uptake were lower in clusterin KO mice in the high fat-fed group. The plasma levels of clusterin and clusterin mRNA levels in the skeletal muscle and liver were increased by the high-fat diet. The mRNA levels of the antioxidant enzymes were lower, and the mRNA levels of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 1 and cytokines and protein carbonylation were higher in the skeletal muscle and liver in clusterin KO mice after the high-fat diet. Palmitate-induced gene expressions of NOX1 and cytokines were higher in the primary cultured hepatocytes of clusterin KO mice compared with the wild-type mice. Clusterin inhibited the gene expression and reactive oxygen species generation by palmitate in the hepatocytes and C2C12. AKT phosphorylation by insulin was reduced in the hepatocytes of clusterin KO mice. These results suggest that clusterin plays a protective role against high-fat diet-induced insulin resistance through the suppression of oxidative stress and inflammation.

HDL functionality

PURPOSE OF REVIEW

HDL cholesterol concentration is inversely correlated with cardiovascular disease and has a wide range of functions involved in many systems. The purpose of this review is to summarize HDL functionality, its relevance to atherosclerosis and factors affecting HDL functions.

RECENT FINDINGS

The contribution of HDL to reverse cholesterol transport may not be as great as first envisaged. However, it still plays an important role in cholesterol efflux from peripheral tissues. The capacity of HDL to promote cellular cholesterol efflux in an ex-vivo model has been reported to correlate more closely with carotid intima-media thickness than HDL cholesterol concentration. Recently, a variety of other functions of HDL have been described including antimicrobial, antioxidant, antiglycation, anti-inflammatory, nitric oxide--inducing, antithrombotic and antiatherogenic activity and immune modulation as well as a potential role in glucose homeostasis, diabetes pathophysiology and complications.

SUMMARY

HDL has a wide range of functions some of which are independent of its cholesterol content. Its cargo of apolipoproteins, various proteins and phospholipids contributes most to its various functions. These functions are affected by a number of genetic, physiological and pathological factors.

Plasma apolipoprotein levels are associated with cognitive status and decline in a community cohort of older individuals

Objectives

Apolipoproteins have recently been implicated in the etiology of Alzheimer’s disease (AD). In particular, Apolipoprotein J (ApoJ or clusterin) has been proposed as a biomarker of the disease at the pre-dementia stage. We examined a group of apolipoproteins, including ApoA1, ApoA2, ApoB, ApoC3, ApoE, ApoH and ApoJ, in the plasma of a longitudinal community based cohort.

Methods

664 subjects (257 with Mild Cognitive Impairment [MCI] and 407 with normal cognition), mean age 78 years, from the Sydney Memory and Aging Study (MAS) were followed up over two years. Plasma apolipoprotein levels at baseline (Wave 1) were measured using a multiplex bead fluorescence immunoassay technique.

Results

At Wave 1, MCI subjects had lower levels of ApoA1, ApoA2 and ApoH, and higher levels of ApoE and ApoJ, and a higher ApoB/ApoA1 ratio. Carriers of the apolipoprotein E ε4 allele had significantly lower levels of plasma ApoE, ApoC3 and ApoH and a significantly higher level of ApoB. Global cognitive scores were correlated positively with ApoH and negatively with ApoJ levels. ApoJ and ApoE levels were correlated negatively with grey matter volume and positively with cerebrospinal fluid (CSF) volume on MRI. Lower ApoA1, ApoA2 and ApoH levels, and higher ApoB/ApoA1 ratio, increased the risk of cognitive decline over two years in cognitively normal individuals. ApoA1 was the most significant predictor of decline. These associations remained after statistically controlling for lipid profile. Higher ApoJ levels predicted white matter atrophy over two years.

Conclusions

Elderly individuals with MCI have abnormal apolipoprotein levels, which are related to cognitive function and volumetric MRI measures cross-sectionally and are predictive of cognitive impairment in cognitively normal subjects. ApoA1, ApoH and ApoJ are potential plasma biomarkers of cognitive decline in non-demented elderly individuals.

SREBP-1c regulates glucose-stimulated hepatic clusterin expression

Clusterin is a stress-response protein that is involved in diverse biological processes, including cell proliferation, apoptosis, tissue differentiation, inflammation, and lipid transport. Its expression is upregulated in a broad spectrum of diverse pathological states. Clusterin was recently reported to be associated with diabetes, metabolic syndrome, and their sequelae. However, the regulation of clusterin expression by metabolic signals was not addressed. In this study we evaluated the effects of glucose on hepatic clusterin expression. Interestingly, high glucose concentrations significantly increased clusterin expression in primary hepatocytes and hepatoma cell lines, but the conventional promoter region of the clusterin gene did not respond to glucose stimulation. In contrast, the first intronic region was transcriptionally activated by high glucose concentrations. We then defined a glucose response element (GlRE) of the clusterin gene, showing that it consists of two E-box motifs separated by five nucleotides and resembles carbohydrate response element (ChoRE). Unexpectedly, however, these E-box motifs were not activated by ChoRE binding protein (ChREBP), but were activated by sterol regulatory element binding protein-1c (SREBP-1c). Furthermore, we found that glucose induced recruitment of SREBP-1c to the E-box of the clusterin gene intronic region. Taken together, these results suggest that clusterin expression is increased by glucose stimulation, and SREBP-1c plays a crucial role in the metabolic regulation of clusterin.

Association of apolipoprotein J polymorphism 1598delT with coronary artery disease and lipoprotein levels

OBJECTIVES

To investigate a polymorphism of the apolipoprotein J (APOJ) gene in relation to coronary artery disease (CAD) and lipid variables in a Chinese male population of genetically unrelated individuals.

METHODS

In this study, we recruited 126 control male subjects and 237 CAD male patients. CAD was defined as a fixed stenotic lesion with luminal narrowing ≥50% in at least one of the major or minor coronary arteries. In cases with documented myocardial infarction, only those rated as fully recovered for more than 3 months were enrolled. Patients with acute or chronic infectious diseases and those with malignancies were excluded. All subjects with a fasting serum triglyceride level higher than 300 mg/dl were likewise excluded.

RESULTS

We identified a single nucleotide polymorphism, 1598delT, and showed its association with CAD. Subjects with the I/I genotype showed a significantly higher CAD risk compared to those with the D/D genotype (OR 2.34, 95% CI 1.11-4.94, p = 0.026). Patients with the I/I genotype also had abnormal levels of high-density lipoprotein-cholesterol and low-density lipoprotein-cholesterol associated with CAD.

CONCLUSIONS

Our data indicated that the APOJ single nucleotide polymorphism (1598delT) is associated with risk factors for CAD in a Chinese population.

Plasma proteomic profiles of bovine growth hormone transgenic mice as they age

Attenuation of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis results in extended lifespan in many organisms including mice. Conversely, GH transgenic mice have excess GH action and die prematurely. We have studied bovine (b) GH transgenic mice (n = 9) and their wild type (WT) littermates (n = 8) longitudinally and have determined several age-related changes. Compared to WT mice, bGH mice lost fat mass, became hypoglycemic and had lower insulin levels at older ages despite being hyperinsulinemic when young. To examine plasma protein differences in bGH mice relative to controls, samples at 2, 4, 8, 12 and 16 months of age were analyzed by two-dimensional gel electrophoresis followed by identification using mass spectrometry. We found several differences in plasma proteins of bGH mice compared to controls, including increased apolipoprotein E (five isoforms), haptoglobin (four isoforms) and mannose-binding protein-C (one out of three isoforms), and decreased transthyretin (six isoforms). In addition, clusterin (two out of six isoforms) and haptoglobin (four isoforms) were up-regulated in bGH mice as a function of age. Finally, alpha-2 macroglobulin (seven isoforms) was altered in an isoform-specific manner with two isoforms increased and two decreased in bGH mouse plasma compared to controls. In conclusion, identification of these proteins suggests that bGH mice exhibit an increased inflammatory state with an adverse lipid profile, possibly contributing to their diminished life expectancy. Also, these newly discovered plasma proteins may be indicative or 'biomarkers' of a shortened lifespan.

Essential role of clusterin in pancreas regeneration

Based on our previous observations that clusterin induction accompanies pancreas regeneration in the rat, we sought to determine if regeneration might be impaired in mice that lacked clusterin. We studied the impact of absent clusterin on morphogenic and functional features of regenerating pancreas. Clusterin induction was accompanied in the regenerating pancreas by a robust development of new lobules with ductules, acini, and endocrine islets in wild type after partial pancreatectomy. In clusterin knock-out mice, however, pancreatectomy resulted in a poor formation of regenerating lobule. In particular, regeneration of beta-cells was also significantly reduced and was associated with persistent hyperglycemia. Duct cells obtained from pancreatectomized clusterin knock-out mice exhibited impaired beta-cell formation in vitro; this was restored by administration of exogenous clusterin. We suggest that clusterin plays a critical role to promote both exocrine and endocrine regeneration following pancreas injury, as well as for in vitro beta-cell regeneration.

Clusterin synergizes with IL-2 for the expansion and IFN-γ production of natural killer cells

CLU is a secreted, multifunctional protein implicated in several immunologic and pathologic conditions. As the level of serum CLU was shown to be elevated during inflammatory responses, we questioned if CLU might interact with circulating lymphocytes leading to functional consequences. To assess this possibility directly, mouse splenocytes and purified NK cells were cultured with varying dose of CLU, and its effect on cell proliferation was examined. Our data showed that CLU up-regulated DNA synthesis and expansion of NK cells significantly in response to a suboptimal, but not maximal, dose of IL-2, and CLU alone did not exhibit such effects. This CLU-mediated synergy required the co-presence of CLU at the onset of IL-2 stimulation and needed a continuous presence during the rest of the culture. Importantly, NK cells stimulated with CLU showed increased formation of cell clusters and a CD69 activation receptor, representing a higher cellular activation status compared with those from the control group. Furthermore, these NK cells displayed elevated IFN-γ production upon RMA/S tumor target exposures, implying that CLU regulates not only NK cell expansion but also effector function of NK cells. Collectively, our data present a previously unrecognized function of CLU as a novel regulator of NK cells via providing costimulation required for cell proliferation and IFN-γ secretion. Therefore, the role of CLU on NK cells should be taken into consideration for the previously observed, diverse functions of CLU in chronic inflammatory and autoimmune conditions.

Toll-like receptor 3 mediates expression of clusterin/apolipoprotein J in vascular smooth muscle cells stimulated with RNA released from necrotic cells

Clusterin/Apolipoprotein J is a protein that is upregulated in a broad spectrum of diverse pathological processes. The predominant form is a secreted glycoprotein (sCLU) with cytoprotective and anti-inflammatory properties which shows enhanced expression in vascular smooth muscle cells (VSMC) following aortic injury and in atherosclerotic disease. Recent evidence indicates that during atherosclerosis, Toll-like receptors (TLRs) are activated in vascular cells by endogenous ligands. Here, we analyzed whether CLU expression in VSMC is controlled by TLRs, and stimulated by factors associated with or released by necrotic cells. Activation of TLR3 by the synthetic RNA analogue polyinosinic-polycytidylic acid (poly(I:C)) in CRL2018 VSMC and in mice led to induction of CLU mRNA and protein synthesis, respectively. In TLR3-deficient 10A yolk sac cells, induction of CLU by poly(I:C) challenge depended on the ectopic expression of human TLR3. In mice lacking the TLR3-signaling adaptor protein TRIF (TIR-domain-containing adaptor protein inducing IFN-β) CLU induction by poly(I:C) was abrogated. In addition to poly(I:C) CLU gene expression in CRL2018 cells was induced by purified cellular RNA and RNA present in necrotic cell lysate. Our data indicate that cellular RNA following its release from necrotic cells in atherosclerotic lesions can act as an endogenous TLR3 ligand to induce CLU expression in VSMC and in vivo. Thus, they expand the view on TLR2 and TLR4 as known pro-atherosclerotic effectors toward TLR3. Conclusively, TLR3 activation induces expression of cytoprotective and anti-inflammatory CLU by VSMC and mice, to potentially counteract atherosclerotic pathology.

Identification of human plasma proteins as major clients for the extracellular chaperone clusterin

Clusterin (CLU) is an extracellular chaperone that is likely to play an important role in protein folding quality control. This study identified three deposition disease-associated proteins as major plasma clients for clusterin by studying CLU-client complexes formed in response to physiologically relevant stress (shear stress, approximately 36 dynes/cm(2) at 37 degrees C). Analysis of plasma samples by size exclusion chromatography indicated that (i) relative to control plasma, stressed plasma contained proportionally more soluble protein species of high molecular weight, and (ii) high molecular weight species were far more abundant when proteins purified by anti-CLU immunoaffinity chromatography from stressed plasma were compared with those purified from control plasma. SDS-PAGE and Western blot analyses indicated that a variety of proteins co-purified with CLU from both stressed and control plasma; however, several proteins were uniquely present or much more abundant when plasma was stressed. These proteins were identified by mass spectrometry as ceruloplasmin, fibrinogen, and albumin. Immunodot blot analysis of size exclusion chromatography fractionated plasma suggested that CLU-client complexes generated in situ are very large and may reach >or=4 x 10(7) Da. Lastly, sandwich enzyme-linked immunosorbent assay detected complexes containing CLU and ceruloplasmin, fibrinogen, or albumin in stressed but not control plasma. We have previously proposed that CLU-client complexes serve as vehicles to dispose of damaged misfolded extracellular proteins in vivo via receptor-mediated endocytosis. A better understanding of these mechanisms is likely to ultimately lead to the identification of new therapies for extracellular protein deposition disorders.

Chapter 2: Clusterin (CLU): From one gene and two transcripts to many proteins

Clusterin (CLU) has kept many researchers engaged for a long time since its first discovery and characterization in the attempt to unravel its biological role in mammals. Although there is a general consensus on the fact that CLU is supposed to play important roles in nearly all fundamental biological phenomena and in many human diseases including cancer, after about 10 years of work CLU has been defined as an "enigmatic" protein. This sense of frustration among the researchers is originated by the fact that, despite considerable scientific production concerning CLU, there is still a lack of basic information about the complex regulation of its expression. The CLU gene is a single 9-exon gene expressed at very different levels in almost all major tissues in mammals. The gene produces at least three protein forms with different subcellular localization and diverse biological functions. The molecular mechanism of production of these protein forms remains unclear. The best known is the glycosylated mature form of CLU (sCLU), secreted with very big quantitative differences at different body sites. Hormones and growth factors are the most important regulators of CLU gene expression. Before 2006, it was believed that a unique transcript of about 1.9 kb was originated by transcription of the CLU gene. Now we know that alternative transcriptional initiation, possibly driven by two distinct promoters, may produce at least two distinct CLU mRNA isoforms differing in their unique first exon, named Isoform 1 and Isoform 2. A third transcript, named Isoform 11036, has been recently found as one of the most probable mRNA variants. Approaches like cloning, expression, and functional characterization of the different CLU protein products have generated a critical mass of information teaching us an important lesson about CLU gene expression regulation. Nevertheless, further studies are necessary to better understand the tissue-specific regulation of CLU expression and to identify the specific signals triggering the expression of different/alternative transcript isoforms and protein forms in different cell types at appropriate time.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Proteome Profiling of Vitreoretinal Diseases by Cluster Analysis

Vitreous samples collected in retinopathic surgeries have diverse properties, making proteomics analysis difficult. We report a cluster analysis to evade this difficulty. Vitreous and subretinal fluid samples were collected from 60 patients during surgical operation of non-proliferative diabetic retinopathy, proliferative diabetic retinopathy, proliferative vitreoretinopathy, and rhegmatogenous retinal detachment. For controls we collected vitreous fluid from patients of idiopathic macular hole, epiretinal, and from a healthy postmortem donor. Proteins from these samples were subjected to quantitative proteomics using two-dimensional gel electrophoresis. We selected 105 proteins robustly expressed among ca 400 protein spots and subjected them to permutation test. By using permutation test analysis we observed unique variations in the expression of some of these proteins in vitreoretinal diseases when compared to the control and to each other: 1) the levels of inflammation-associate proteins such as AAT, APOA4, ALB, and TF were significantly higher in all four types of vitreoretinal diseases, and 2) each vitreoretinal disease elevates a unique set of proteins which can be interpreted based on the pathology of retinopathy. Our protocol will be effective for the study of protein expression in other types of clinical samples of diverse property.

Traumatic brain injury induces biphasic upregulation of ApoE and ApoJ protein in rats

Apolipoproteins play an important role in cell repair and have been found to increase shortly after traumatic brain injury (TBI). In addition, apolipoproteins reduce amyloid-beta (Abeta) accumulation in models of Alzheimer's disease. Considering that TBI induces progressive neurodegeneration including Abeta accumulation, we explored potential long-term changes in the gene and protein expression of apolipoproteins E and J (ApoE and J) over 6 months after injury. Anesthetized male Sprague-Dawley rats were subjected to parasagittal fluid-percussion brain injury and their brains were evaluated at 2, 4, 7, 14 days, and 1 and 6 months after TBI. In situ hybridization, Western blot, and immunohistochemical analysis demonstrated that although there was a prolonged upregulation in both the gene expression and protein concentration of ApoE and J after injury, these responses were uncoupled. Upregulation of ApoE and J mRNA expression lasted from 4 days to 1 month after injury. In contrast, a biphasic increase in protein concentration and number of immunoreactive cells for ApoE and ApoJ was observed, initially peaking at 2 days (i.e., before increased mRNA expression), returning to baseline by 2 weeks and then gradually increasing through 6 months postinjury. In addition, ApoE and J were found to colocalize with Abeta accumulation in neurons and astrocytes at 1-6 months after injury. Collectively, these data suggest that ApoE and J play a role in the acute sequelae of brain trauma and reemerge long after the initial insult, potentially to modulate progressive neurodegenerative changes.

Serum Apolipoprotein J in Health, Coronary Heart Disease and Type 2 Diabetes Mellitus

Apolipoprotein (apo) J, clusterin, is ubiquitously expressed in many tissues, and is a component of high-density lipoproteins (HDLs). There is experimental evidence that it may be anti-atherogenic through its effects on cholesterol transport, smooth muscle cell proliferation and lipid peroxidation. HDLs containing apo J and apo A-I carry paraoxonase (PON1), which protects low-density lipoproteins from oxidative modification; however, the extent to which apo J affects coronary heart disease (CHD) is not known. We have developed a sandwich ELISA that enables apo J to be assayed in the range of 13-200 microg/mL. Serum apo J was 52.8+/-0.8 microg/mL (mean+/-SEM; range, 36.0-84.3 microg/mL; n=92) in healthy Japanese men, and 49.3+/-0.5 microg/mL (34.5-72.8; n=241) in healthy Japanese women. Multiple regression of these data and results from 67 men with CHD showed that apo J concentration was unrelated to age, sex or body mass index, but was positively related to serum PON1 (p<0.001) and apo B (p<0.02) concentrations. In women, it was also positively related to blood glucose (p<0.02). After adjusting for its associations with covariates, serum apo J averaged 5.4 microg/mL, lower in CHD men than in controls (p<0.003). Type 2 diabetics had higher apo J concentrations (men, 83.1+/-3.4 microg/mL, n=64; women, 64.0+/-2.3 microg/mL, n=46) than healthy men and women (p<0.001). In these Type 2 diabetics, apo J concentration was unrelated to PON1 concentration, but was positively related to blood glucose (p<0.01). After adjustment for its relation to blood glucose, the mean apo J concentration was similar in diabetics and healthy subjects. These findings suggest that apo J may be anti-atherogenic in humans, and that its concentration is raised by Type 2 diabetes.

Hemorrhagic shock induces differential gene expression and apoptosis in mouse liver

Comprehensive knowledge of the gene expression changes induced by hemorrhage in vital organs will greatly improve prognosis and therapy. Therefore, we used a mouse model of non-resuscitated hemorrhagic shock to study the pattern of stress-induced genes in liver at 1, 4, and 24 h following surgery. Hepatic injury was confirmed by assessment of liver injury markers and apoptotic cell death. We found that a variety of stress-regulated genes were differentially expressed, including seven genes that have not been reported previously as being regulated by hemorrhagic shock: ATF-2, alphaB-crystallin, GADD45, GADD45beta, Mdm2, p21Waf1, and TRPM-2. The changes in mRNA levels of the transcription factors AP-1, Egr-1, HSF-1, and NF-kappaB were transient but protein expression was noticeable at later time points. Our findings show that oxidative stress causes immediate upregulation of genes involved in a variety of cellular defense pathways. Complex interactions among them might determine the ultimate fate of the cell.

Thematic review series: The Immune System and Atherogenesis. Lipoprotein-associated inflammatory proteins: markers or mediators of cardiovascular disease?

In humans, a chronically increased circulating level of C-reactive protein (CRP), a positive acute-phase reactant, is an independent risk factor for cardiovascular disease. This observation has led to considerable interest in the role of inflammatory proteins in atherosclerosis. In this review, after discussing CRP, we focus on the potential role in the pathogenesis of human vascular disease of inflammation-induced proteins that are carried by lipoproteins. Serum amyloid A (SAA) is transported predominantly on HDL, and levels of this protein increase markedly during acute and chronic inflammation in both animals and humans. Increased SAA levels predict the risk of cardiovascular disease in humans. Recent animal studies support the proposal that SAA plays a role in atherogenesis. Evidence is accruing that secretory phospholipase A(2), an HDL-associated protein, and platelet-activating factor acetylhydrolase, a protein associated predominantly with LDL in humans and HDL in mice, might also play roles both as markers and mediators of human atherosclerosis. In contrast to positive acute-phase proteins, which increase in abundance during inflammation, negative acute-phase proteins have received less attention. Apolipoprotein A-I (apoA-I), the major apolipoprotein of HDL, decreases during inflammation. Recent studies also indicate that HDL is oxidized by myeloperoxidase in patients with established atherosclerosis. These alterations may limit the ability of apoA-I to participate in reverse cholesterol transport. Paraoxonase-1 (PON1), another HDL-associated protein, also decreases during inflammation. PON1 is atheroprotective in animal models of hypercholesterolemia. Controversy over its utility as a marker of human atherosclerosis may reflect the fact that enzyme activity rather than blood level (or genotype) is the major determinant of cardiovascular risk. Thus, multiple lipoprotein-associated proteins that change in concentration during acute and chronic inflammation may serve as markers of cardiovascular disease. In future studies, it will be important to determine whether these proteins play a causal role in atherogenesis.

[Paraoxonase, something more than an enzyme?]

Coronary heart disease is one of the major causes of death in developed countries. The hypothesis that peroxidation of low density lipoproteins (LDL) may be the initial step of the atherosclerotic process has promoted numerous studies aimed at investigating the mechanisms by which the body protects itself from such oxidative phenomena. Among these mechanisms we find the paraoxanase (PON) enzyme, which is quite thriving the last decades. This enzyme is principally associated with high density lipoproteins (HDL) but it also seems to help LDL to recover their antioxidant status. This paper reviews different aspects concerning the mechanisms implicated in the induction and activity of this enzyme, as well as its production, attachment to HDL, and modifications of its activity due to external factors. The use of genetic techniques, the study of the polimorphisms of the PON enzyme and the possibility of increasing paraoxonase activity by means of pharmacotherapy and/or dietary therapy open new perspectives with regard to coronary heart disease treatment and prevention.

Alterations in the post-translational modification and intracellular trafficking of clusterin in MCF-7 cells during apoptosis

Clusterin is a heterodimeric, disulfide-linked 70-80 kDa glycoprotein that is induced during regression of most, if not all, hormone-dependent epithelial tissues. These studies describe the biogenesis and intracellular trafficking of clusterin in MCF-7 cells before and after the initiation of apoptosis with antiestrogens and TNF alpha. Under physiological conditions, clusterin is modified in the endoplasmic reticulum (ER), and proteolytically cleaved in the Golgi to generate discrete alpha and beta chains prior to secretion. Treatment with TNFalpha or the antiestrogen, ICI 182,780, induces apoptosis in MCF-7 cells and leads to substantial changes in the activity of Golgi-resident enzymes, significantly altering the biogenesis of clusterin. This leads to the appearance of a 50-53 kDa uncleaved, nonglycosylated, disulfide-linked isoform of clusterin that accumulates in the nucleus. While clusterin contains a cryptic SV-40-like nuclear localization signal, mutation of this sequence does not affect the nuclear accumulation of the disulfide-linked nuclear isoform. Confocal microscopy demonstrates that the nuclear accumulation of clusterin is coincident with DNA fragmentation. These data suggest that, at least in secretory epithelial cells, retrograde transport from the Golgi to the ER of a nonglycosylated, uncleaved isoform and the subsequent translocation of clusterin to the nucleus occur in dying cells.

Synthesis and functional analyses of nuclear clusterin, a cell death protein

Nuclear clusterin (nCLU) is an ionizing radiation (IR)-inducible protein that binds Ku70, and triggers apoptosis when overexpressed in MCF-7 cells. We demonstrate that endogenous nCLU synthesis is a product of alternative splicing. Reverse transcriptase-PCR analyses revealed that exon II, containing the first AUG and encoding the endoplasmic reticulum-targeting peptide, was omitted. Exons I and III are spliced together placing a downstream AUG in exon III as the first available translation start site. This shorter mRNA produces the 49-kDa precursor nCLU protein. Ku70 binding activity was localized to the C-terminal coiled-coil domain of nCLU. Leucine residues 357, 358, and 361 of nCLU were necessary for Ku70-nCLU interaction. The N- and C-terminal coiled-coil domains of nCLU interacted with each other, suggesting that the protein could dimerize or fold. Mutation analyses indicate that the C-terminal NLS was functional in nCLU with the same contribution from N-terminal NLS. The C-terminal coiled-coil domain of nCLU was the minimal region required for Ku binding and apoptosis. MCF-7 cells show nuclear as well as cytoplasmic expression of GFP-nCLU in apoptotic cells. Cytosolic aggregation of GFP-nCLU was found in viable cells. These results indicate that an inactive precursor of nCLU exists in the cytoplasm of non-irradiated MCF-7 cells, translocates into the nucleus following IR, and induces apoptosis.

Serum levels of the senescence biomarker clusterin/apolipoprotein J increase significantly in diabetes type II and during development of coronary heart disease or at myocardial infarction

Clusterin/apolipoprotein J (hereafter ApoJ) is a conserved secreted glycoprotein expressed by a wide array of tissues and being implicated in several physiological processes. ApoJ has been shown to associate with both normal in vitro aging, namely replicative senescence, as well as with stress induced premature senescence. In vivo, the protein is up-regulated in many severe physiological disturbances that relate to advanced aging, including accumulation in the artery wall during the development of atherosclerosis. In the current report we have expanded our previous studies that focus in the biological role of ApoJ during aging by addressing two interrelated issues: (a) we have examined the potential ApoJ association with in vivo aging and (b) we have studied whether its accumulation in the artery wall during the development of atherosclerosis is combined with a measurable increase of its serum levels, as well as, whether a similar effect occurs in diseases, such as diabetes type II, known to represent major risk factors of atherosclerosis. By combining a sandwich ELISA assay and immunoblotting analysis we demonstrate a measurable increase of ApoJ serum levels with age in males and provide evidence that, as compared to healthy donors, the serum ApoJ amount increases significantly in diabetic type II patients and in patients suffering from either a developing coronary heart disease, or myocardial infarction. The highest serum ApoJ levels were found during myocardial infarction but no correlation was observed with the number of vessels with documented atherosclerotic damage. In conclusion, this report illustrates that ApoJ accumulation in serum is probably coupled to a generalized stress mediated induction mechanism that is specifically related to certain diseases; moreover these data raise the possibility that elevated ApoJ levels in serum may represent a strong indication of vascular damage.

When X-ray-inducible proteins meet DNA double strand break repair

Cellular responses to ionizing radiation (IR) include (a) activation of signal transduction enzymes; (b) stimulation of DNA repair, most notably DNA double strand break (DSB) repair by homologous or nonhomologous recombinatorial pathways; (c) activation of transcription factors and subsequent IR-inducible transcript and protein changes; (d) cell cycle checkpoint delays in G(1), S, and G(2) required for repair or for programmed cell death of severely damaged cells; (e) activation of zymogens needed for programmed cell death (although IR is a poor inducer of such responses in epithelial cells); and (f) stimulation of IR-inducible proteins that may mediate bystander effects influencing signal transduction, DNA repair, angiogenesis, the immune response, late responses to IR, and possibly adaptive survival responses. The overall response to IR depends on the cell's inherent genetic background, as well as its ability to biochemically and genetically respond to IR-induced damage. To improve the anti-tumor efficacy of IR, our knowledge of these pleiotropic responses must improve. The most important process for the survival of a tumor cell following IR is the repair of DNA double strand breaks (DSBs). Using yeast two-hybrid analyses along with other molecular and cellular biology techniques, we cloned transcripts/proteins that are involved in, or presumably affect, nonhomologous DNA double strand break end-joining (NHEJ) repair mediated by the DNA-PK complex. Using Ku70 as bait, we isolated a number of Ku-binding proteins (KUBs). We identified the first X-ray-inducible transcript/protein (xip8, Clusterin (CLU)) that associates with DNA-PK. A nuclear form of CLU (nCLU) prevented DNA-PK-mediated end joining, and stimulated cell death in response to IR or when overexpressed in the absence of IR. Structure-function analyses using molecular and cellular (including green fluorescence-tagged protein trafficking) biology techniques showed that nCLU appears to be an inactive protein residing in the cytoplasm of epithelial cells. Following IR injury, nCLU levels increase and an as yet undefined posttranslational modification appears to alter the protein, exposing nuclear localization sequences (NLSs) and coiled-coil domains. The modified protein translocates to the nucleus and triggers cell death, presumably through its interaction specifically with Ku70. Understanding nCLU responses, as well as the functions of the KUBs, will be important for understanding DSB repair. Knowledge of DSB repair may be used to improve the antitumor efficacy of IR, as well as other chemotherapeutic agents.

Immunolocalization of apolipoproteins in aortic atherosclerosis in American youths and young adults: findings from the PDAY study

The immunohistochemical distribution of apolipoproteins in the abdominal aortas of 142 men, 15-34 years of age, collected in a cooperative multicenter study group (Pathobiological Determinants of Atherosclerosis in Youth) was examined in relationship to serum VLDL+LDL+HDL cholesterol levels. ApoB deposits were limited to the intima of specimens with intimal fibro cellular thickening or atherosclerotic lesions. Apo A-I, E and J were observed in both the intima and media of the aortas with intimal lesions. The pattern of apoJ distribution was similar to that of apoA-I and E. The distribution patterns of these apolipoproteins in these young adults were very similar to those in adults and old men seen in an earlier study. The extent of apolipoprotein distribution in the intima and media increased with age and the stage of atherosclerosis development, but was not correlated significantly with serum VLDL+LDL or HDL cholesterol levels. The infiltration of lipoprotein particles into the aortic wall seems to be more strongly associated with the progression of intimal lesions rather than with serum cholesterol levels.

Increased expression of GPI-specific phospholipase D in mouse models of type 1 diabetes

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is a high-density lipoprotein-associated protein. However, the tissue source(s) for circulating GPI-PLD and whether serum levels are regulated are unknown. Because the diabetic state alters lipoprotein metabolism, and liver and pancreatic islets are possible sources of GPI-PLD, we hypothesized that GPI-PLD levels would be altered in diabetes. GPI-PLD serum activity and liver mRNA were examined in two mouse models of type 1 diabetes, a nonobese diabetic (NOD) mouse model and low-dose streptozotocin-induced diabetes in CD-1 mice. With the onset of hyperglycemia (2- to 5-fold increase over nondiabetic levels), GPI-PLD serum activity and liver mRNA increased 2- to 4-fold in both models. Conversely, islet expression of GPI-PLD was absent as determined by immunofluorescence. Insulin may regulate GPI-PLD expression, because insulin treatment of diabetic NOD mice corrected the hyperglycemia along with reducing serum GPI-PLD activity and liver mRNA. Our data demonstrate that serum GPI-PLD levels are altered in the diabetic state and are consistent with liver as a contributor to circulating GPI-PLD.

Apoptotic cell debris and phosphatidylserine-containing lipid vesicles induce apolipoprotein J (clusterin) gene expression in vital fibroblasts

The molecular events in cells undergoing programmed cell death (apoptosis) are well studied; however, the response of the surviving neighbor cells to local cell death is largely uncharacterized. Apolipoprotein J (clusterin) is an 80-kDa glycoprotein that has been implied in cytoprotection of the vital cells, presumably by assisting in the clearance of apoptotic vesicles and membrane remnants. Its mRNA is specifically up-regulated in the vital cells of apoptotic tissues. The molecular mechanisms, however, leading to this response are not known. We here show that exposure of vital fibroblasts to apoptotic vesicles, disrupted vital cells, and trypsin-treated membrane remnants induces apoJ mRNA. Moreover, lipid vesicles consisting of phosphatidylserine (PtSer) and dimyristoylphosphatidylcholine (PC), but not liposomes with PC alone nor with dimyristoylphosphatidylethanolamine or phosphatidic acid, did elevate apoJ mRNA level. These results suggest that, apart from mediating the endocytic uptake of the apoptotic vesicles, PtSer also serves as a trigger to stimulate the expression of genes that might be involved in the cellular clearance process.

Apolipoprotein J/clusterin limits the severity of murine autoimmune myocarditis

Apolipoprotein J/clusterin (apoJ/clusterin), an intriguing protein with unknown function, is induced in myocarditis and numerous other inflammatory injuries. To test its ability to modify myosin-induced autoimmune myocarditis, we generated apoJ-deficient mice. ApoJ-deficient and wild-type mice exhibited similar initial onset of myocarditis, as evidenced by the induction of two early markers of the T cell-mediated immune response, MHC-II and TNF receptor p55. Furthermore, autoantibodies against the primary antigen cardiac myosin were induced to the same extent. Although the same proportion of challenged animals exhibited some degree of inflammatory infiltrate, inflammation was more severe in apoJ-deficient animals. Inflammatory lesions were more diffuse and extensive in apoJ-deficient mice, particularly in females. In marked contrast to wild-type animals, the development of a strong generalized secondary response against cardiac antigens in apoJ-deficient mice was predictive of severe myocarditis. Wild-type mice with a strong Ab response to secondary antigens appeared to be protected from severe inflammation. After resolution of inflammation, apoJ-deficient, but not wild-type, mice exhibited cardiac function impairment and severe myocardial scarring. These results suggest that apoJ limits progression of autoimmune myocarditis and protects the heart from postinflammatory tissue destruction.

Isolation and characterization of apolipoproteins from murine microglia. Identification of a low density lipoprotein-like apolipoprotein J-rich but E-poor spherical particle

Amyloid Abeta deposition is a neuropathologic hallmark of Alzheimer's disease. Activated microglia are intimately associated with plaques and appear to facilitate Abeta deposition, an event believed to contribute to pathogenesis. It is unclear if microglia can modulate pathogenesis of Alzheimer's disease by secreting lipoprotein particles. Here we show that cultured BV2 murine microglial cells, like astrocytes, secrete apolipoprotein E (apoE) and apolipoprotein J (apoJ) in a time-dependent manner. To isolate and identify BV2 microglial particles, gel filtration chromatography was employed to fractionate BV2-conditioned medium. Analyses by Western blot, lipid determination, electron microscopy, and native gel electrophoresis demonstrate that BV2 microglial cells release spherical low density lipoprotein (LDL)-like lipid-containing particles rich in apoJ but poor in apoE. These microglial particles are dissimilar in size, shape, and lipoprotein composition to astrocyte-derived particles. The microglial-derived particles were tested for functional activity. Under conditions of suppressed de novo cholesterol synthesis, the LDL-like particles effectively rescued primary rat cortical neurons from mevastatin-induced neurotoxicity. The particles were also shown to bind Abeta. We speculate that the LDL-like apoJ-rich apoE-poor microglial lipoproteins preferentially bind the lipoprotein receptor, recognizing apoJ, which is abundant in the choroid plexus, facilitating Abeta clearance from the brain. BV2 cells also secrete an apoE-rich lipid-poor species that binds Abeta. Consistent with the role of apoE in Abeta fibril formation and deposition, this microglial species may promote plaque formation.

Identification of clusterin sequences mediating renal tubular cell interactions

Expression of the glycoprotein clusterin is markedly increased following tissue injury. One function of clusterin is to promote cell interactions which are perturbed in these pathologic settings. Clusterin causes cell aggregation and adhesion in vitro yet the molecular mechanism for this effect is not known. In order to identify the active site(s) of clusterin, 34 peptides, each 15 amino acid residues in length, were synthesized from hydrophilic regions of human clusterin. When studied individually, none of the peptides caused aggregation of LLC-PK1 cells, a porcine renal epithelial cell line. However, two out of the 34 peptides inhibited clusterin-induced cell aggregation in a dose-dependent manner. Scrambled versions of these two 'active' peptides did not inhibit cell aggregation. Seven peptides promoted cell adhesion. In conclusion, these findings provide evidence for novel amino acid sequences mediating clusterin-induced renal cell interactions.

Clusterin in the male reproductive system: localization and possible function

Clusterin is a glycoprotein that was initially isolated from the male reproductive system. Subsequently, clusterin has been found to be widely distributed in a variety of tissues in mammals. One characteristic of the expression of clusterin is that it is induced as a result of cellular injury, death, or pathology. Despite the efforts of many laboratories working in diverse biological systems, the function of clusterin remains unknown. Recent studies have revealed a 'heat-shock element' in the promoter of the gene that may account for the inducible nature of the clusterin gene. Overall, the evidence suggests that function of clusterin is to protect surviving cells after damage. This protection may result from a detergent-like action of the protein.

Multiple involvement of clusterin in chicken ovarian follicle development. Binding to two oocyte-specific members of the low density lipoprotein receptor gene family

The interaction of the female germ cell with somatic cells during the development of the ovarian follicle in the chicken provides a prime system to study gene expression. Here, we have uncovered the involvement of clusterin, the function(s) of which is still poorly understood, in this complex process. As revealed by molecular cloning, chicken clusterin is a 428-residue protein that migrates at 70 kDa on SDS-polyacrylamide gel electrophoresis and possesses most of the structural features of its mammalian successors. However, in contrast to mammalian clusterin, the chicken protein appears not to be cleaved intracellularly into a disulfide-linked heterodimer; possibly as a consequence thereof, it is not secreted constitutively and is absent from the circulation, where most of clusterin is found in mammals. In the ovary, clusterin is a major product of the somatic granulosa cells, in a pattern correlating with the developmental phases of individual follicles. In that, transcript levels are high not only at onset of vitellogenesis, but also in atretic follicles and in the postovulatory follicle sac, i.e. in situations characterized by apoptotic events. Yolk of growing oocytes contains a 43-kDa truncated form of clusterin that does not appear to be synthesized within the oocyte. Rather, we here show for the first time that 70-kDa clusterin interacts not only with megalin, but also with two chicken oocyte-specific members of the low density lipoprotein receptor (LDLR) gene family. These receptors, termed LDLR-related protein with eight ligand binding repeats (LR8) and LDLR-related protein (380 kDa), likely internalize granulosa cell-derived 70-kDa clusterin, which may subsequently be processed to the 43-kDa product. Thus, chicken clusterin could serve as a marker for follicular atresia and resorption, and, based on its ability to bind several other proteins, it may serve as carrier for the receptor-mediated endocytosis into oocytes of components important for embryonic development, two hitherto unknown functions of this intriguing protein.

Dissociation of apolipoprotein and apolipoprotein receptor response to lesion in the rat brain: an in situ hybridization study

The epsilon4 allele of apolipoprotein E is associated with increased risk for developing Alzheimer's disease. To further understand the anatomical distribution of apolipoprotein E and its native receptors in the brain, we studied their messenger RNA expression in the adult rat brain under normal conditions and in response to an excitotoxic lesion to the hippocampus. In situ hybridization using oligonucleotide probes for apolipoprotein E, apolipoprotein J, the low density lipoprotein receptor, very low density lipoprotein receptor, low density lipoprotein receptor related protein, 39,000 mol. wt receptor-associated protein and glycoprotein 330/Megalin messenger RNA were performed on adjacent sections throughout the rat forebrain. Apolipoprotein E messenger RNA was abundantly expressed in the rat brain in both white and gray matter localizing to astrocytes but not neurons. Low density lipoprotein receptor-related protein and receptor-associated protein messenger RNA had a similar regional distribution but low density lipoprotein receptor-related protein messenger RNA was expressed by both neurons and glia, while the expression of receptor-associated protein messenger RNA was more highly expressed in neurons. Apolipoprotein J messenger RNA was expressed by neurons, glia and choroid plexus. The low density lipoprotein receptor and very low density lipoprotein receptor messenger RNA were found in both neurons and glia. Glycoprotein 330/Megalin messenger RNA was not detectable in the adult rat brain. In response to hippocampal lesions, apolipoprotein E and apolipoprotein J messenger RNAs were significantly up-regulated seven and 11 days post-lesion but the expression of low density lipoprotein receptor, low density lipoprotein receptor-related protein, receptor-associated protein, glycoprotein 330/Megalin, and very low density lipoprotein receptor messenger RNAs were unchanged. The expression of apolipoprotein E messenger RNA increased gradually beginning at three days while the expression of apolipoprotein J messenger RNA began to increase at seven days post-lesion. These findings further implicate apolipoproteins in the response of the brain to injury in vivo and suggest that transcriptional up-regulation of the apolipoprotein receptors studied is not a prominent feature in the response.

Identification of multiple genes with altered expression at the distal anastomosis of healing polytetrafluoroethylene grafts

PURPOSE

Anastomotic intimal hyperplasia remains a significant cause of delayed prosthetic arterial graft failure. Prior studies have identified several genes with altered expression within the hyperplastic region at the downstream polytetrafluoroethylene arterial anastomosis as compared with normal arteries. The purpose of the current study was to determine the sequence of early gene-related events at the distal anastomosis of an in vivo prosthetic arterial graft model. Messenger RNA (mRNA) differential display was used to screen for alterations in gene expression between anastomotic sites and control arterial segments.

METHODS

Six carotid interposition 6-mm expanded polytetrafluoroethylene grafts were placed in mongrel dogs, with the intervening carotid artery segment serving as the baseline control. Five days after graft implantation, the distal anastomotic artery segments were harvested and total RNA was isolated from both the intervening normal arteries and anastomotic segments. Differential mRNA display was used to identify candidate complementary DNA (cDNA) clones with expression that differed in anastomotic segments as compared with normal intervening arteries. Northern blot analysis confirmed alteration of gene expression. The cDNA clones were sequenced, and gene databases were searched. Novel sequences were used as probes for screening human cDNA libraries.

RESULTS

Approximately 7000 mRNA species were screened, and 26 candidate clones were obtained. Northern blot analysis showed altered gene expression in 10 (38%) of the clones, undetectable signals in 13 (50%), and nonregulation in 3 (12%). Seven clones with 92% homology at the nucleotide level to human alpha1 (III) procollagen gene and novel sequence were expressed only at the distal anastomosis. A clone representing apolipoprotein J and a novel sequence had increased expression at the distal anastomosis of 364% +/- 236% and 156% +/- 47%, respectively (mean percentage, control +/- standard deviation).

CONCLUSIONS

These studies identified genes with expressions that increased or were exclusive to the distal anastomosis of healing prosthetic arterial grafts in an in vivo prosthetic arterial graft model. Type III collagen may contribute significantly to the composition of the extracellular matrix associated with intimal hyperplasia by increasing lesion volume. Apolipoprotein J, through its association with proteases, may modulate some of the matrix changes seen early after grafting.

Distribution and synthesis of apolipoprotein J in the atherosclerotic aorta

The distribution of apolipoprotein (apo) J during the development of atherosclerosis in the human aorta was evaluated by immununohistochemical observation, together with the other apolipoprotein A-I, A-II, B, C-III, and E. Although apoJ was never observed in the normal aorta (ie, without any intimal lesions or intimal thickening), it was distributed not only in the intima but also in the media of aortas with diffuse, intimal thickening or atherosclerotic lesions. Double immunostaining with antibodies for apoJ and alpha-smooth muscle actin revealed apoJ deposition in smooth muscle cells (SMCs) or the aortic stroma in the vicinity of SMCs. The extent of apoJ distribution in the aortic wall increased with the degree of atherosclerosis development. In addition, the distribution pattern of apoJ was very similar to that of apoA-I and E. In situ hybridization with human apoJ cDNA demonstrated intense signals in cells scattered within the subendothelial space and medial SMCs of the aorta with advanced atherosclerosis but not in those of the normal aorta without intimal thickening. Furthermore, reverse transcriptase-polymerase chain reaction of the cultured human aortic SMCs revealed apoJ mRNA expression in these cells. The results indicate that apoJ in the aortic wall originates from not only apoJ circulated in the plasma but also apoJ produced by SMCs in the aortic wall. Considering the similarities of the distribution between apoJ and apo-A-I or E, we hypothesize that apoJ possibly has a protective role against human atherosclerosis by its involvement with cholesterol transport from the aortic wall to the liver.

Analysis of an expression profile of genes in the human adipose tissue

Increasing evidence suggests that in addition to storing excess energy as fat, adipose tissue acts as an endocrine organ secreting various factors into the blood stream. Every time a new factor is found in adipose tissue, however, its implication is discussed independently, and a systematic analyses based upon a global view of gene expression of this tissue has not been performed. To describe the function of this tissue in terms of gene expression, and to find new factors, we performed random complementary DNA (cDNA) sequencing using a 3'-directed cDNA library that faithfully represents the composition of the messenger RNA (mRNA). Various well-known but unexpected genes, including those for gelsolin, plasma glutathione peroxidase (GPX-3) and carboxypeptidase E (CPE) were shown to be very active. By comparing the expression profile of active genes in the adipose with those of other tissues and with data in dbEST, we identified seven new genes that are specifically expressed in adipose tissue. Among these, one encoded a protein with collagen-like repeats and a putative secretion signal. These data can be used as new tools for analyses of the physiology of this tissue, as well as the etiology and complications of obesity.

Clusterin and the terminal complement pathway synthesized by human umbilical vein endothelial cells are closely linked when detected on co-cultured agarose beads

Clusterin and the terminal complement pathway synthesized by human umbilical vein endothelial cells are closely linked when detected on co-cultured agarose beads. Clusterin is a multifunctional regulatory protein rendering the terminal complement complex (TCC) soluble and unable to insert into cell membranes. The aim of the present study was to examine whether clusterin was an integral part of serum-derived TCC bound to agarose beads which activate the alternative pathway of complement. Further, we searched for evidence of clusterin synthesis in human umbilical vein endothelial cells (EC) and whether this synthesis was regulated by various proinflammatory cytokines (IL-1, IL-6, and TNF) and IFN-gamma. The clusterin and TCC on co-incubated beads were measured by radioimmunoassay based on primary anti-complement antibodies (anti-C3c, anti-TCC, anti-clusterin). We found that clusterin in serum experiments is bound to C9 in agarose bound TCC and not directly to the agarose. Addition of the protein synthesis inhibitor cycloheximide to cultured human umbilical vein cells resulted in a strong reduction (about 70%) of anti-clusterin binding to co-cultured beads, which strongly supports de novo synthesis of clusterin in EC. The results indicate that clusterin derived from the EC is linked with the TCC on the co-incubated beads for the following reasons: First, in serum experiments clusterin like vitronectin, was co-deposited with C9 in agarose-bound TCC. Second, cytokine stimulation of the EC with proinflammatory cytokines such as IL-1, IL-6 and TNF, known to increase the detection of bound TCC, also increased the amount of clusterin detected on the beads. Third, IFN-gamma, which reduces the concentration of bound TCC, exhibited the same effect on the amount of clusterin detected on such beads. There was a strong and dose-dependent reduction of anti-TCC binding from about 45% to about 95% when clusterin (5-40 micrograms/ml) was added to EC cultures. This effect was also evident (about 40-50% inhibition of bound TCC) using human serum as complement source. These results are probably mainly caused by clusterin binding to C5b-7, making this complex soluble without the capacity to bind to the agarose surface. This study supports the view that clusterin is a potent regulator of TCC at the levels of C5b-7 and C9.

Clusterin: physiologic and pathophysiologic considerations

Clusterin is a heterodimeric glycoprotein produced by a wide array of tissues and found in most biologic fluids. A number of physiologic functions have been proposed for clusterin based on its distribution and in vitro properties. These include complement regulation, lipid transport, sperm maturation, initiation of apoptosis, endocrine secretion, membrane protection, and promotion of cell interactions. A prominent and defining feature of clusterin is its induction in such disease states as glomerulonephritis, polycystic kidney disease, renal tubular injury, neurodegenerative conditions including Alzheimer's disease, atherosclerosis, and myocardial infarction. The expression of clusterin in these states is puzzling, from the specific molecular species and cellular pathways eliciting such expression, to the roles subserved by clusterin once induced. This review will discuss these physiologic and pathophysiologic aspects of clusterin and speculate on its role in disease.

Local synthesis of apolipoprotein J in the eye

Apolipoprotein J (apoJ), a secretory glycoprotein known to transport lipids and to regulate terminal complement function, is present in the human eye in both aqueous and vitreous, as well as in the retina. Ocular apoJ is the product of local synthesis, rather than plasma contamination, as demonstrated by its distinct structural properties and the presence of abundant apoJ mRNA in retina and retina pigment epithelium. ApoJ mRNA is also present in mouse eye, with a developmentally regulated pattern of expression. In fetal mouse, apoJ mRNA is present in retina, lens and cornea. In contrast, adult eye apoJ mRNA is present in retina and ciliary body. We propose that apoJ is important in tissue remodeling and in stabilizing hydrophobic molecules which are required for vision and/or which would otherwise be deleterious and membrane-active.