Murine clusterin: molecular cloning and mRNA localization of a gene associated with epithelial differentiation processes during embryogenesis

Regulation of psoriasis, colitis, and the intestinal microbiota by clusterin

Psoriasis, a chronic and systemic inflammatory disorder characterized by activation of the interleukin (IL)-23/IL-17 axis, may be associated with the intestinal microbiota through the so-called "gut-skin axis." Clusterin is a glycoprotein ubiquitously distributed in mammalian tissues; however, its role in psoriasis is unclear. Therefore, we evaluated the role of clusterin in psoriatic skin inflammation, systemic inflammation, and colitis using a murine model of IMQ-induced psoriasis. In IMQ-treated clusterin-knockout (clusterin-/-) mice, the expressions of inflammatory cytokines in clusterin-silenced human keratinocytes and intestinal microbial composition were analyzed. We also examined clusterin expression in the skin tissues of patients with psoriasis. IMQ-induced psoriatic skin inflammation is suppressed in clusterin-/- mice. Long-term administration of IMQ induced systemic inflammation and colitis; however, both were alleviated by the genetic deletion of clusterin. Genetic silencing of clusterin in human keratinocytes inhibited the production of inflammatory cytokines involved in the initiation and progression of psoriasis. The composition of the intestinal microbiota in IMQ-treated clusterin-/- and wild-type mice was different. Genetic deletion of clusterin suppressed the increase in the Firmicutes/Bacteroidetes (F/B) ratio. Skin tissues of patients with psoriasis showed high clusterin expression. In conclusion, inhibition of clusterin decreased psoriatic skin inflammation, systemic inflammation, colitis, and altered the F/B ratio in an IMQ-induced murine psoriasis model.

The Ins and Outs of Clusterin: Its Role in Cancer, Eye Diseases and Wound Healing

Clusterin (CLU) is a glycoprotein originally discovered in 1983 in ram testis fluid. Rapidly observed in other tissues, it was initially given various names based on its function in different tissues. In 1992, it was finally named CLU by consensus. Nearly omnipresent in human tissues, CLU is strongly expressed at fluid-tissue interfaces, including in the eye and in particular the cornea. Recent research has identified different forms of CLU, with the most prominent being a 75-80 kDa heterodimeric protein that is secreted. Another truncated version of CLU (55 kDa) is localized to the nucleus and exerts pro-apoptotic activities. CLU has been reported to be involved in various physiological processes such as sperm maturation, lipid transportation, complement inhibition and chaperone activity. CLU was also reported to exert important functions in tissue remodeling, cell-cell adhesion, cell-substratum interaction, cytoprotection, apoptotic cell death, cell proliferation and migration. Hence, this protein is sparking interest in tissue wound healing. Moreover, CLU gene expression is finely regulated by cytokines, growth factors and stress-inducing agents, leading to abnormally elevated levels of CLU in many states of cellular disturbance, including cancer and neurodegenerative conditions. In the eye, CLU expression has been reported as being severely increased in several pathologies, such as age-related macular degeneration and Fuch's corneal dystrophy, while it is depleted in others, such as pathologic keratinization. Nevertheless, the precise role of CLU in the development of ocular pathologies has yet to be deciphered. The question of whether CLU expression is influenced by these disorders or contributes to them remains open. In this article, we review the actual knowledge about CLU at both the protein and gene expression level in wound healing, and explore the possibility that CLU is a key factor in cancer and eye diseases. Understanding the expression and regulation of CLU could lead to the development of novel therapeutics for promoting wound healing.

Exploring the translational potential of clusterin as a biomarker of early osteoarthritis

BACKGROUND

Clusterin (CLU; also known as apolipoprotein J) is an ATP-independent holdase chaperone that prevents proteotoxicity as a consequence of protein aggregation. It is a ∼60 kDa disulfide-linked heterodimeric protein involved in the clearance of cellular debris and the regulation of apoptosis. CLU has been proposed to protect cells from cytolysis by complement components and has been implicated in Alzheimer's disease due to its ability to bind amyloid-β peptides and prevent aggregate formation in the brain. Recent studies suggest that CLU performs moonlighting functions. CLU exists in two major forms: an intracellular form and a secreted extracellular form. The intracellular form of CLU may suppress stress-induced apoptosis by forming complexes with misfolded proteins and facilitates their degradation. The secreted form of CLU functions as an extracellular chaperone that prevents protein aggregation.

METHODS

In this review, we discuss the published literature on the biology of CLU in cartilage, chondrocytes, and other synovial joint tissues. We also review clinical studies that have examined the potential for using this protein as a biomarker in synovial and systemic fluids of patients with rheumatoid arthritis (RA) or osteoarthritis (OA).

RESULTS

Since CLU functions as an extracellular chaperone, we propose that it may be involved in cytoprotective functions in osteoarticular tissues. The secreted form of CLU can be measured in synovial and systemic fluids and may have translational potential as a biomarker of early repair responses in OA.

CONCLUSION

There is significant potential for investigating synovial and systemic CLU as biomarkers of OA. Future translational and clinical orthopaedic studies should carefully consider the diverse roles of this protein and its involvement in other comorbidities. Therefore, future biomarker studies should not correlate circulating CLU levels exclusively to the process of OA pathogenesis and progression. Special attention should be paid to CLU levels in synovial fluid.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

There is significant potential for investigating synovial and systemic CLU as a predictive biomarker of osteoarthritis (OA) progression and response to novel treatments and interventions. Given that CLU plays diverse roles in other comorbidities such as rheumatoid arthritis (RA) and obesity, future translational and clinical orthopaedic biomarker studies should not directly correlate circulating CLU levels to the process of OA pathogenesis and progression. However, special attention should be paid to CLU levels in synovial fluid. The cytoprotective properties of CLU may support the implementation of regenerative strategies and new approaches for developing targeted therapeutics for OA.

A single-cell interactome of human tooth germ from growing third molar elucidates signaling networks regulating dental development

Background

Development of dental tissue is regulated by extensive cell crosstalk based on various signaling molecules, such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) pathways. However, an intact network of the intercellular regulation is still lacking.

Result

To gain an unbiased and comprehensive view of this dental cell interactome, we applied single-cell RNA-seq on immature human tooth germ of the growing third molar, discovered refined cell subtypes, and applied multiple network analysis to identify the central signaling pathways. We found that immune cells made up over 80% of all tooth germ cells, which exhibited profound regulation on dental cells via Transforming growth factor-β, Tumor necrosis factor (TNF) and Interleukin-1. During osteoblast differentiation, expression of genes related to extracellular matrix and mineralization was continuously elevated by signals from BMP and FGF family. As for the self-renewal of apical papilla stem cell, BMP-FGFR1-MSX1 pathway directly regulated the G0-to-S cell cycle transition. We also confirmed that Colony Stimulating Factor 1 secreted from pericyte and TNF Superfamily Member 11 secreted from osteoblast regulated a large proportion of genes related to osteoclast transformation from macrophage and monocyte.

Conclusions

We constructed the intercellular signaling networks that regulated the essential developmental process of human tooth, which served as a foundation for future dental regeneration engineering and the understanding of oral pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00691-5.

Diverse functions of clusterin promote and protect against the development of pulmonary fibrosis

Pulmonary fibrosis is a progressive scarring disorder of the lung with dismal prognosis and no curative therapy. Clusterin, an extracellular chaperone and regulator of cell functions, is reduced in bronchoalveolar lavage fluid of patients with pulmonary fibrosis. However, its distribution and role in normal and fibrotic human lung are incompletely characterized. Immunohistochemical localization of clusterin revealed strong staining associated with fibroblasts in control lung and morphologically normal areas of fibrotic lung but weak or undetectable staining in fibrotic regions and particularly fibroblastic foci. Clusterin also co-localized with elastin in vessel walls and additionally with amorphous elastin deposits in fibrotic lung. Analysis of primary lung fibroblast isolates in vitro confirmed the down-regulation of clusterin expression in fibrotic compared with control lung fibroblasts and further demonstrated that TGF-β1 is capable of down-regulating fibroblast clusterin expression. shRNA-mediated down-regulation of clusterin did not affect TGF-β1-induced fibroblast-myofibroblast differentiation but inhibited fibroblast proliferative responses and sensitized to apoptosis. Down-regulation of clusterin in fibrotic lung fibroblasts at least partly due to increased TGF-β1 may therefore represent an appropriate but insufficient response to limit fibroproliferation. Reduced expression of clusterin in the lung may also limit its extracellular chaperoning activity contributing to dysregulated deposition of extracellular matrix proteins.

Clusterin and Pycr1 alterations associate with strain and model differences in susceptibility to experimental pancreatitis

Acute pancreatitis has several underlying etiologies, and results in consequences ranging from mild to complex multi-organ failure. The wide range of pathology suggests a genetic predisposition for progression. We compared the susceptibility to acute pancreatitis in BALB/c and FVB/N mice, coupled with proteomic analysis, in order to identify potential protein associations with pancreatitis progression.

METHODS

Pancreatitis was induced in BALB/c and FVB/N mice by administration of cerulein or feeding a choline-deficient, ethionine-supplemented (CDE) diet. Histology and changes in serum amylase were examined. Proteome profiling in cerulein-treated mice was performed using 2-dimensional differential in gel electrophoresis (2D-DIGE) followed by mass spectrometry analysis and biochemical validation.

RESULTS

Male and female FVB/N mice manifested more severe cerulein-induced pancreatitis as compared with BALB/c mice, but both strains were similarly susceptible to CDE-induced pancreatitis. Few of the 2D-DIGE alterations were validated by immunoblotting. Clusterin was markedly up-regulated after cerulein-induced pancreatitis in FVB/N but less-so in BALB/c mice. Pyrroline-5-carboxylate reductase (Pycr1), an enzyme involved in proline biosynthesis, had higher basal levels in FVB/N male and female mouse pancreata compared with BALB/c pancreata, and was relatively more resistant to degradation in FVB/N pancreata. However, serum and pancreas tissue proline levels were similar in the two strains.

CONCLUSION

FVB/N is more susceptible than BALB/c mice to cerulein-induced but not CDE-induced pancreatitis. Most of the 2D-DIGE alterations in the two strains likely relate to posttranslational modifications rather than protein level differences. Clusterin levels increase dramatically in association with pancreatitis severity, while Pycr1 is higher in FVB/N versus BALB/c pancreata basally and after induction of pancreatitis. Changes in proline metabolism may represent a novel potential genetic modifier in the context of pancreatitis.

Evaluation of kidney injury biomarkers in rat amniotic fluid after gestational exposure to cadmium

Cadmium is a well-characterized nephrotoxic agent that is also capable of accumulating and diffusing across the placenta; however, only a few studies have addressed its effects over fetal kidneys and none of them has used a panel of sensitive and specific biomarkers for the detection of kidney injury. The goal of this study was to determine cadmium renal effects in rat fetuses by the quantification of early kidney injury biomarkers. Pregnant Wistar rats were exposed by inhalation to an isotonic saline solution or to CdCl2 solution (DDel =1.48 mg Cd kg(-1) day(-1) ) during gestational days (GD) 8-20. On GD 21, dams were euthanized and samples obtained. Kidney injury biomarkers were quantified in amniotic fluid samples and fetal kidneys were microscopically evaluated to search for histological alterations. Our results showed that cadmium exposure significantly raised albumin, osteopontin, vascular endothelial growth factor and tissue inhibitor of metalloproteinases-1 levels in amniotic fluid, whereas it decreased creatinine. Clusterin, calbindin and IFN-inducible protein 10 did not show any change. Accordingly, histological findings showed tubular damage and precipitations in the renal pelvis. In conclusion, gestational exposure to cadmium induces structural alterations in fetal renal tissue that can be detected by some kidney injury biomarkers in amniotic fluid samples. Copyright © 2016 John Wiley & Sons, Ltd.

Distinct promoters, subjected to epigenetic regulation, drive the expression of two clusterin mRNAs in prostate cancer cells

The human clusterin (CLU) gene codes for several mRNAs characterized by different sequences at their 5' end. We investigated the expression of two CLU mRNAs, called CLU 1 and CLU 2, in immortalized (PNT1a) and tumorigenic (PC3 and DU145) prostate epithelial cells, as well as in normal fetal fibroblasts (WI38) following the administration of the epigenetic drugs 5-aza-2'-deoxycytidine (AZDC) and trichostatin A (TSA) given either as single or combined treatment (AZDC-TSA). Our experimental evidences show that: a) CLU 1 is the most abundant transcript variant. b) CLU 2 is expressed at a low level in normal fibroblasts and virtually absent in prostate cancer cells. c) CLU 1, and to a greater extent CLU 2 expression, increased by AZDC-TSA treatment in prostate cancer cells. d) Both CLU 1 and CLU 2 encode for secreted CLU. e) P2, a novel promoter that overlaps the CLU 2 Transcription Start Site (TSS), drives CLU 2 expression. f) A CpG island, methylated in prostate cancer cells and not in normal fibroblasts, is responsible for long-term heritable regulation of CLU 1 expression. g) ChIP assay of histone tail modifications at CLU promoters (P1 and P2) shows that treatment of prostate cancer cells with AZDC-TSA causes enrichment of Histone3(Lys9)acetylated (H3K9ac) and reduction of Histone3(Lys27)trimethylated (H3K27me3), inducing active transcription of both CLU variants. In conclusion, we show for the first time that the expression of CLU 2 mRNA is driven by a novel promoter, P2, whose activity responds to epigenetic drugs treatment through changes in histone modifications.

Clusterin is a potential lymphotoxin beta receptor target that is upregulated and accumulates in germinal centers of mouse spleen during immune response

Clusterin is a multifunctional protein that participates in tissue remodeling, apoptosis, lipid transport, complement-mediated cell lysis and serves as an extracellular chaperone. The role of clusterin in cancer and neurodegeneration has been extensively studied, however little is known about its functions in the immune system. Using expression profiling we found that clusterin mRNA is considerably down-regulated in mouse spleen stroma upon knock-out of lymphotoxin β receptor which plays pivotal role in secondary lymphoid organ development, maintenance and function. Using immunohistochemistry and western blot we studied clusterin protein level and distribution in mouse spleen and mesenteric lymph nodes in steady state and upon immunization with sheep red blood cells. We showed that clusterin protein, represented mainly by the secreted heterodimeric form, is present in all stromal compartments of secondary lymphoid organs except for marginal reticular cells. Clusterin protein level rose after immunization and accumulated in light zones of germinal centers in spleen--the effect that was not observed in lymph nodes. Regulation of clusterin expression by the lymphotoxin beta signaling pathway and its protein dynamics during immune response suggest a specific role of this enigmatic protein in the immune system that needs further study.

Promotion of cell proliferation by clusterin in the renal tissue repair phase after ischemia-reperfusion injury

Renal repair begins soon after the kidney suffers ischemia-reperfusion injury (IRI); however, its molecular pathways are not fully understood. Clusterin (Clu) is a chaperone protein with cytoprotective functions in renal IRI. The aim of this study was to investigate the role of Clu in renal repair after IRI. IRI was induced in the left kidneys of wild-type (WT) C57BL/6J (B6) vs. Clu knockout (KO) B6 mice by clamping the renal pedicles for 28–45 min at the body temperature of 32°C. The renal repair was assessed by histology and confirmed by renal function. Gene expression was examined using PCR array. Here, we show that following IRI, renal tubular damage and Clu expression in WT kidneys were induced at day 1, reached the maximum at day 3, and significantly diminished at day 7 along with normal function, whereas the tubular damage in Clu KO kidneys steadily increased from initiation of insult to the end of the experiment, when renal failure occurred. Renal repair in WT kidneys was positively correlated with an increase in Ki67+ proliferative tubular cells and survival from IRI. The functions of Clu in renal repair and renal tubular cell proliferation in cultures were associated with upregulation of a panel of genes that could positively regulate cell cycle progression and DNA damage repair, which might promote cell proliferation but not involve cell migration. In conclusion, these data suggest that Clu is required for renal tissue regeneration in the kidney repair phase after IRI, which is associated with promotion of tubular cell proliferation.

Lung epithelial branching program antagonizes alveolar differentiation

Mammalian organs, including the lung and kidney, often adopt a branched structure to achieve high efficiency and capacity of their physiological functions. Formation of a functional lung requires two developmental processes: branching morphogenesis, which builds a tree-like tubular network, and alveolar differentiation, which generates specialized epithelial cells for gas exchange. Much progress has been made to understand each of the two processes individually; however, it is not clear whether the two processes are coordinated and how they are deployed at the correct time and location. Here we show that an epithelial branching morphogenesis program antagonizes alveolar differentiation in the mouse lung. We find a negative correlation between branching morphogenesis and alveolar differentiation temporally, spatially, and evolutionarily. Gain-of-function experiments show that hyperactive small GTPase Kras expands the branching program and also suppresses molecular and cellular differentiation of alveolar cells. Loss-of-function experiments show that SRY-box containing gene 9 (Sox9) functions downstream of Fibroblast growth factor (Fgf)/Kras to promote branching and also suppresses premature initiation of alveolar differentiation. We thus propose that lung epithelial progenitors continuously balance between branching morphogenesis and alveolar differentiation, and such a balance is mediated by dual-function regulators, including Kras and Sox9. The resulting temporal delay of differentiation by the branching program may provide new insights to lung immaturity in preterm neonates and the increase in organ complexity during evolution.

A cellular pathway involved in Clara cell to alveolar type II cell differentiation after severe lung injury

Regeneration of alveolar epithelia following severe pulmonary damage is critical for lung function. We and others have previously shown that Scgb1a1-expressing cells, most likely Clara cells, can give rise to newly generated alveolar type 2 cells (AT2s) in response to severe lung damage induced by either influenza virus infection or bleomycin treatment. In this study, we have investigated cellular pathway underlying the Clara cell to AT2 differentiation. We show that the initial intermediates are bronchiolar epithelial cells that exhibit Clara cell morphology and express Clara cell marker, Scgb1a1, as well as the AT2 cell marker, pro-surfactant protein C (pro-SPC). These cells, referred to as pro-SPC(+) bronchiolar epithelial cells (or SBECs), gradually lose Scgb1a1 expression and give rise to pro-SPC(+) cells in the ring structures in the damaged parenchyma, which appear to differentiate into AT2s via a process sharing some features with that observed during alveolar epithelial development in the embryonic lung. These findings suggest that SBECs are intermediates of Clara cell to AT2 differentiation during the repair of alveolar epithelia following severe pulmonary injury.

Expression of Clu and Tgfb1 during murine tooth development: effects of in-vivo transfection with anti-miR-214

Expression of clusterin (Clu) in the murine first molar tooth germ was markedly increased at postnatal developmental stages. The time-course of expression of this gene paralleled those of other genes encoding proteins involved during the secretory phase of odontogenesis, as described previously. Immunohistochemical studies of clusterin in murine molar tooth germs suggested this protein to be located in outer enamel epithelium, regressing enamel organ, secretory ameloblasts, and the dental epithelium connecting the tooth to the oral epithelium at an early eruptive stage. Immunolabelling of transforming growth factor beta-1 (TGF-β1) revealed it to be located close to clusterin. The levels of expression of Clu and Tgfb1 were markedly decreased following in-vivo transfection with anti-miR-214. In contrast, the expression of several genes associated with regulation of growth and development were increased by this treatment. We suggest that clusterin has functions during secretory odontogenesis and the early eruptive phase. Bioinformatic analysis after treatment with anti-miR-214 suggested that, whilst cellular activities associated with tooth mineralization and eruption were inhibited, activities associated with an alternative developmental activity (i.e. biosynthesis of contractile proteins) appeared to be stimulated. These changes probably occur through regulation mediated by a common cluster of transcription factors and support suggestions that microRNAs (miRNAs) are highly significant as regulators of differentiation during odontogenesis.

Decreased plasma levels of clusterin in patients with psoriasis

INTRODUCTION AND OBJECTIVES

Psoriasis is a chronic inflammatory disease that has been linked to increased cardiovascular risk. The glycoprotein clusterin (apolipoprotein J) is a component of high-density lipoproteins and has a protective role in atherosclerosis. The aim of the present study was to evaluate the plasma levels of clusterin and the proinflammatory cytokine macrophage migration inhibitory factor (MIF) in patients with severe psoriasis, comparing groups of patients with different risks of cardiovascular disease.

MATERIAL AND METHODS

Twenty-one patients with severe psoriasis (psoriasis area severity index and body surface area>10) and 11 healthy controls with no dermatologic disease were studied. Cardiovascular risk factors were assessed according to the Adult Treatment Panel (ATP) III criteria. Subclinical carotid atheromatosis was assessed by Doppler ultrasonography of the carotid arteries. Plasma clusterin and MIF levels were measured by enzyme-linked immunosorbent assay.

RESULTS

ATP-III criteria for metabolic syndrome were met by 47% of the patients, and 33% had carotid atheromatous plaque. Mean (SD) clusterin plasma levels were significantly lower in patients with psoriasis compared with controls (81.39 [27.30] μg/mL for the 21 patients vs 117 [21.6] μg/mL for the 11 controls; P=.0017). MIF plasma levels (ng/ml) were significantly higher in patients with atheromatous plaque compared with controls (53.22 [29.02] for the 6 patients with plaque vs 34.21 [9.65] for the 11 controls; P=.0394).

CONCLUSIONS

The decreased plasma levels of clusterin in psoriatic patients suggested an association with the disease and might be an indicator of systemic inflammatory activity. Increased levels of MIF appear to be associated with cardiovascular risk factors and carotid atheromatous plaque.

Gene Expression Profiling during Murine Tooth Development

The aim of this study was to describe the expression of genes, including ameloblastin (Ambn), amelogenin X chromosome (Amelx), and enamelin (Enam) during early (pre-secretory) tooth development. The expression of these genes has predominantly been studied at post-secretory stages. Deoxyoligonucleotide microarrays were used to study gene expression during development of the murine first molar tooth germ at 24 h intervals, starting at the 11th embryonic day (E11.5), and up to the 7th day after birth (P7). The profile search function of Spotfire software was used to select genes with similar expression profile as the enamel genes (Ambn, Amelx, and Enam). Microarray results where validated using real-time reverse transcription-polymerase chain reaction (real-time RT-PCR), and translated proteins identified by Western-blotting. In situ localization of the Ambn, Amelx, and Enam mRNAs were monitored from E12.5 to E17.5 using deoxyoligonucleotide probes. Bioinformatics analysis was used to associate biological functions with differentially expressed (DE; p ≤ 0.05) genes. Microarray results showed a total of 4362 genes including Ambn, Amelx, and Enam to be significant DE throughout the time-course. The expression of the three enamel genes was low at pre-natal stages (E11.5–P0) increasing after birth (P1–P7). Profile search lead to isolation of 87 genes with significantly similar expression to the three enamel proteins. These mRNAs were expressed in dental epithelium and epithelium derived cells. Although expression of Ambn, Amelx, and Enam were lower during early tooth development compared to secretory stages enamel proteins were detectable by Western-blotting. Bioinformatic analysis associated the 87 genes with multiple biological functions. Around 35 genes were associated with 15 transcription factors.

Dietary oil modifies the plasma proteome during aging in the rat

Fatty acids and other components of the diet may modulate, among others, mechanisms involved in homeostasis, aging, and age-related diseases. Using a proteomic approach, we have studied how dietary oil affected plasma proteins in young (6 months) or old (24 months) rats fed lifelong with two experimental diets enriched in either sunflower or virgin olive oil. After the depletion of the most abundant proteins, levels of less abundant proteins were studied using two-dimensional electrophoresis and mass spectrometry. Our results showed that compared with the sunflower oil diet, the virgin olive oil diet induced significant decreases of plasma levels of acute phase proteins such as inter-alpha inhibitor H4P heavy chain (at 6 months), hemopexin precursor (at 6 and 24 months), preprohaptoglobin precursor (at 6 and 24 months), and α-2-HS glycoprotein (at 6 and 24 months); antioxidant proteins such as type II peroxiredoxin (at 24 months); proteins related with coagulation such as fibrinogen γ-chain precursor (at 24 months), T-kininogen 1 precursor (at 6 and 24 months), and apolipoprotein H (at 6 and 24 months); or with lipid metabolism and transport such as apolipoprotein E (at 6 and 24 months) and apolipoprotein A-IV (at 24 months). The same diet increased the levels of apolipoprotein A-1 (at 6 and 24 months), diminishing in general the changes that occurred with age. Our unbiased analysis reinforces the beneficial role of a diet rich in virgin olive oil compared with a diet rich in sunflower oil, modulating inflammation, homeostasis, oxidative stress, and cardiovascular risk during aging.

Clusterin in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a ubiquitous multifunctional glycoprotein. Following its identification in 1983, clusterin was found to be clearly increased in Alzheimer's disease (AD). Later research demonstrated that clusterin could bind amyloid-beta (Abeta) peptides and prevent fibril formation, a hallmark of AD pathology. In addition to preventing excessive inflammation, intracellular clusterin was found to reduce apoptosis and oxidative stress. Although early studies were inconclusive, two recent large-scale genome-wide association studies (GWAS) independently identified variants within the clusterin gene as risk factors for developing AD. This review focuses on the characteristics of clusterin and possible mechanisms of its relationship to AD.

Preclinical perspective of urinary biomarkers for the detection of nephrotoxicity: what we know and what we need to know

The assessment of kidney damage is a challenge and must incorporate assessment of the functional capacity of the kidney, as well as a comprehensive understanding of the kidney's role. Multiple parameters have been used for many years to measure renal functionality to assess renal damage. It is astonishing that, beside histopathology, the most common traditional parameters are serum based. However, urine is also used to obtain additional information regarding the health status of the kidneys. Since 2008, several novel urinary protein biomarkers have been qualified by the US FDA and the European Medicines Agency in conjunction with the Predictive Safety Testing Consortium in a specially developed qualification process. Subsequently, the Pharmaceuticals and Medical Devices Agency accepted the qualification of these seven urinary biomarkers. This review will give an overview of the state-of-the-art detection based on urinary biomarkers, which will enhance toxicological research in the future. In addition, the qualification process that leads to acceptance of these biomarkers will be described because of its uniqueness and importance for the field of biomarker research.

Acute effects of thymoquinone on the pregnant rat and embryo-fetal development

The effect of a single intraperitoneal (i.p.) injection of thymoquinone (TQ) on the pregnant rat and embryo-fetal development was investigated. Pregnant female Wistar rats received 15, 35, and 50 mg/kg body weight of TQ i.p. on day 11 or 14 of gestation, and on day 18 of gestation they were sacrificed and laparotomized. Results showed that TQ induces maternal and embryonic toxicities in a dose- and time-dependent manner. With a dose of 50 mg/kg, treated rats experienced a significant decrease in maternal body weight and complete fetal resorption when the dose was given on day 11 of gestation. On the other hand, 46.2% of implants were resorbed and the viable fetuses showed no TQ-related malformations when the dose was given on day 14 of gestation. At a lower TQ dose of 35 mg/kg, maternal and embryonic toxicities were observed only when it was given on day 11 of gestation. The dose of 15 mg/kg was considered to be a dose with no observed adverse effect level for maternal and embryo-fetal toxicities when it was given day 11 or 14 of gestation. Based on the results of this study, TQ, at doses of 50 and 35 mg/kg, has a potentially disruptive effect on embryonic development during the second trimester of rat pregnancy.

Membrane attack by complement: the assembly and biology of terminal complement complexes

Complement system activation plays an important role in both innate and acquired immunity. Activation of the complement and the subsequent formation of C5b-9 channels (the membrane attack complex) on the cell membranes lead to cell death. However, when the number of channels assembled on the surface of nucleated cells is limited, sublytic C5b-9 can induce cell cycle progression by activating signal transduction pathways and transcription factors and inhibiting apoptosis. This induction by C5b-9 is dependent upon the activation of the phosphatidylinositol 3-kinase/Akt/FOXO1 and ERK1 pathways in a Gi protein-dependent manner. C5b-9 induces sequential activation of CDK4 and CDK2, enabling the G1/S-phase transition and cellular proliferation. In addition, it induces RGC-32, a novel gene that plays a role in cell cycle activation by interacting with Akt and the cyclin B1-CDC2 complex. C5b-9 also inhibits apoptosis by inducing the phosphorylation of Bad and blocking the activation of FLIP, caspase-8, and Bid cleavage. Thus, sublytic C5b-9 plays an important role in cell activation, proliferation, and differentiation, thereby contributing to the maintenance of cell and tissue homeostasis.

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 (CLU) and lung cancer

Lung cancer is the leading cause of cancer-related mortality. It is categorized into two histological groups that have distinct clinical behaviors, the nonsmall cell lung cancers (NSCLC) and the small cell lung cancer (SCLC). When identified at an early stage, NSCLC is treated by surgical resection. However, patients who undergo surgical resection still have a relative low survival rate, primarily for tumor recurrence. Unfortunately, advances in cytotoxic therapy have reached a plateau and new approaches to treatment are needed together with new and better parameters for more accurate prediction of the outcome and more precise indication of the efficacy of the treatment. Several in vitro studies have examined the role of Clusterin (CLU) in carcinogenesis, lung cancer progression, and response to chemo- and radiotherapy. Studies performed in lung cancer cell lines and animal models showed that CLU is upregulated after exposure to chemo- and radiotherapy. A potential role proposed for the protein is cytoprotective. In vitro, CLU silencing by antisense oligonucleotides (ASO) and small-interfering RNAs (siRNA) directed against CLU mRNA in CLU-rich lung cancer cell lines sensitized cells to chemotherapy and radiotherapy and decreased their metastatic potential. In vivo, a recent work analyzed the prognostic role of CLU in NSCLC, showing that CLU-positive patients with lung cancer had a better overall survival and disease-free survival than those with CLU-negative tumors. These data are contradictory to the promising in vitro results. From the results of these studies we may hypothesize that in early-stage lung cancers CLU represents a positive biomarker correlating with better overall survival. In advanced patients, already treated with chemo- and radiotherapy, the induction of CLU may confer resistance to the treatments. However, many studies are needed to better understand the role of CLU in early-stage and advanced lung cancers with the aim to discriminate patients and specific local conditions that could benefit for a CLU knocking down treatment.

A longitudinal study of the protein components of marsupial milk from birth to weaning in the tammar wallaby (Macropus eugenii)

The major milk whey proteins of the tammar wallaby (Macropus eugenii) have been identified over the total period of lactation using proteomic analysis techniques comprising two-dimensional electrophoresis, comparative image analysis, matrix assisted laser desorption ionisation mass spectrometry (MALDI MS), de novo peptide sequencing and cross species protein matching. Samples were collected at the periods coinciding with major milestones of immunological development in the developing marsupial and in the four phases of milk production, specifically, Days 0, 5 (Phase 1); 27, 68 (Phase 2A); 137, 174 (Phase 2B) and 250 (Phase 3). Major changes in the protein content of marsupial milk whey correlated with the changing needs of the pouch young for stages in growth and development. We have shown that the levels of milk whey proteins vary with the developmental stage of the young animal, with a high number of proteins detected in early and late milk compared with the middle phases of lactation. Over 41 proteins were confidently identified, of which most had known roles in immunological protection. Proteins providing immunological protection across the lactation period included transferrin, beta2 microglobulin, haptoglobulin and a 78kDa glucose regulated protein. Immunoglobulin IgJ linker chain and a known antimicrobial cathelicidin, were only detected for the first 100-137 days, after which time Complement B factor was found to be present (Phase 2B). The changes which correlated with development and growth in the pouch young were reflected by the presence of proteins such as an alpha-fetoprotein like protein and clusterin found in early milk (Phase 1-2A) and two unknown proteins which were apparent in very early mammary gland secretions. This is the first comprehensive proteomic study of the major whey proteins of a marsupial across the entire period of lactation and provides fundamental data on proteins secreted by the mammary gland during key stages of immunological development of the young animal.

Inflammatory lipids as a target for therapy in the rheumatic diseases

As patients with autoimmune rheumatic diseases live longer due to improved therapies and preventive measures, death and disability from cardiovascular events are increasing. Patients with rheumatoid arthritis and systemic lupus erythematosus have an increased risk of atherosclerosis that persists even after accounting for traditional cardiac risk factors. Recent studies strongly suggest that the mechanism is due in part to increased levels of oxidized lipids (such as oxidized low density lipoprotein and pro-inflammatory high density lipoproteins) which cause the inflammatory cascade that ultimately leads to plaque formation. The objective of this review is to discuss how inflammatory lipids contribute to the increased risk of atherosclerosis in rheumatoid arthritis and systemic lupus erythematosus, as well as to propose that these oxidized lipids are a rational target for therapeutic intervention in autoimmune diseases. Published literature was examined to review treatments for pro-inflammatory lipids in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. In conclusion, it is possible that these oxidized lipids may also contribute to increased disease manifestations in rheumatic conditions. Several new and existing therapies, including statins and high density lipoprotein-associated protein peptide mimetics such as D-4F (apoA-1) target these oxidized lipids and may be useful in both preventing atherosclerosis and treating inflammation in patients with rheumatic diseases.

FGF10 maintains distal lung bud epithelium and excessive signaling leads to progenitor state arrest, distalization, and goblet cell metaplasia

BACKGROUND

Interaction with the surrounding mesenchyme is necessary for development of endodermal organs, and Fibroblast growth factors have recently emerged as mesenchymal-expressed morphogens that direct endodermal morphogenesis. The fibroblast growth factor 10 (Fgf10) null mouse is characterized by the absence of lung bud development. Previous studies have shown that this requirement for Fgf10 is due in part to its role as a chemotactic factor during branching morphogenesis. In other endodermal organs Fgf10 also plays a role in regulating differentiation.

RESULTS

Through gain-of-function analysis, we here find that FGF10 inhibits differentiation of the lung epithelium and promotes distalization of the embryonic lung. Ectopic expression of FGF10 in the lung epithelium caused impaired lung development and perinatal lethality in a transgenic mouse model. Lung lobes were enlarged due to increased interlobular distance and hyperplasia of the airway epithelium. Differentiation of bronchial and alveolar cell lineages was inhibited. The transgenic epithelium consisted predominantly of proliferating progenitor-like cells expressing Pro-surfactant protein C, TTF1, PEA3 and Clusterin similarly to immature distal tip cells. Strikingly, goblet cells developed within this arrested epithelium leading to goblet cell hyperplasia.

CONCLUSION

We conclude that FGF10 inhibits terminal differentiation in the embryonic lung and maintains the distal epithelium, and that excessive levels of FGF10 leads to metaplastic differentiation of goblet cells similar to that seen in chronic inflammatory diseases.

Analysis of selected transcript levels in porcine spermatozoa, oocytes, zygotes and two-cell stage embryos

It has been suggested that spermatozoa can deliver mRNAs to the oocyte during fertilisation. Using reverse transcription and real-time quantitative polymerase chain reaction analysis (RQ-PCR), we evaluated the presence of clusterin (CLU), protamine 2 (PRM2), calmegin (CLGN), cAMP-response element modulator protein (CREM), methyltransferase 1 (DNMT1), linker histone 1 (H1), protamine 1 (PRM1), TATA box-binding protein associated factor 1 (TAF1) and TATA box-binding protein (TBP) in porcine mature oocytes, zygotes and two-cell stage embryos. Spermatozoa isolated from semen samples of boars contained all transcripts investigated, whereas oocytes contained only CREM, H1, TAF1, and TBP mRNAs. The zygote and two-cell stage embryos contained CLU, CREM, H1, PRM1, PRM2, TAF1 and TBP transcripts. Our observations suggest that porcine spermatozoa may delivery CLU, PRM1 and PRM2 mRNAs to the oocyte, which may contribute to zygotic and early embryonic development.

Clusterin, a novel modulator of TGF-beta signaling, is involved in Smad2/3 stability

Clusterin (CLU) is known as a multifunctional protein involved in a variety of physiological processes including lipid transport, epithelial cell differentiation, tumorigenesis, and apoptosis. It is known that CLU interacts with TGF-beta type ll receptor (TbetaRll). However, the relationship of CLU and TGF-beta signaling is unclear. Here we present that CLU is a novel modulator of TGF-beta signaling by regulating Smad2/3 proteins. Overexpression of CLU enhanced TGF-beta-induced transcriptional activity and increased the amount of Smad2/3 proteins, while CLU siRNA repressed TGF-beta-induced transcriptional activity and decreased the amount of Smad2/3 proteins in Hep3B cells. We also found that CLU was involved in Smad2/3 stability at the protein level. These findings suggest that CLU regulates TGF-beta signaling pathway by modulating the stability of Smad2/3 proteins.

Clusterin/Apolipoprotein J up-regulation after zinc exposure, replicative senescence or differentiation of human haematopoietic cells

Clusterin/Apolipoprotein J (CLU) is a cellular senescence biomarker implicated in several physiological processes. In this work we have investigated CLU expression and function in human haematopoietic cells. We found that early passage human T cell clones (TCC) express minimal endogenous amounts of CLU, which are significantly elevated in late passage cells. Moreover, exposure of TCC to increased levels of the essential micronutrient zinc in culture resulted in intense induction of CLU. Because haematopoietic cells cease proliferation following induction of terminal differentiation, we also studied the expression profile of CLU in the leukemic progenitor cell lines K562 and HL-60. We found that, like TCC, both cell lines express minimal endogenous levels of CLU in their actively proliferating state. However, when induced to differentiate into their distinct cell types, CLU was found to be up-regulated specifically in those cells expressing the main differentiation markers. Enforced stable over-expression of CLU in K562 cells inhibited the expression of the CD14 differentiation marker and blocked differentiation to either monocytes/megacaryoblasts or to erythrocytes. Overall, our results suggest that CLU is actively involved in both replicative senescence and terminal differentiation in different types of human haematopoietic cells.

Cloning and characterization of two clusterin isoforms in rainbow trout

Clusterin is a broadly distributed glycoprotein constitutively expressed by various tissues and cell types and has been shown to be associated with several physiological and pathological functions. In order to study the molecular evolution of clusterin, here we report the cloning and characterization of two clusterin genes in rainbow trout (Oncorhynchus mykiss). The deduced amino acid sequences of clusterin-1 and a partial clusterin-2 clone are 89% identical to each other, showing 45, 42 and 38% identity with chicken, frog and human orthologs, respectively. Most of the putative N-glycosylation sites, as well as all 10 cysteine residues which are involved in disulfide bond formation in the mature trout clusterin-1 protein, are fully conserved when aligned with its orthologs from various species. Although trout clusterin genes exhibit the same exon-intron organization, in line with that of human clusterin, they show a totally different mRNA expression profile among various trout tissues. Phylogenetic analysis indicates an early segregation of the clusterin ancestral gene within the taxon of fish leading to the formation of a separate subgroup.

Clusterin expression can be modulated by changes in TCF1-mediated Wnt signaling

Background

Clusterin (CLU) is an enigmatic molecule associated with various physiological processes and disease states. Different modes of cellular stress lead to increased CLU levels, and additionally numerous growth factors and cytokines affect the expression of the CLU gene. APC and c-MYC, both intimately linked to the Wnt signaling pathway have previously been shown to influence CLU levels, and we therefore investigated if changes in Wnt signaling activity in vitro could regulate the expression of one, or more, of several CLU mRNA and protein variants.

Results

Over-expression of the cytoplasmic domain of E-cadherin tagged with GFP was used to abrogate Wnt signaling activity in LS174T and HCT116 colon carcinoma cells. This fusion construct sequestered signaling competent β-catenin whereby Wnt signaling was abrogated, and consequently cytoplasmic CLU protein levels increased as demonstrated by immunofluorescence. To determine which branch of the Wnt pathway was mediating the CLU response, we over-expressed dominant negative (dn) TCF1 and TCF4 transcription factors in stably transfected LS174T cells. We observed both intra- and extracellular levels of CLU protein to be induced by dnTCF1 but not dnTCF4. Subsequent analysis of the expression levels of three CLU mRNA variants by real time RT-PCR revealed only one CLU mRNA variant to be responsive to dnTCF1 over-expression. 5'-end RACE indicated that this CLU mRNA variant was shorter at the 5'-end than previously reported, and accordingly the translated protein was predicted to be shorter at the N-terminus and destined to the secretory pathway which fit our observations. Examination of the immediate expression kinetics of CLU after dnTCF1 over-expression using real time RT-PCR indicated that CLU might be a secondary Wnt target.

Conclusion

In conclusion, we have demonstrated that the Wnt signaling pathway specifically regulates one out of three CLU mRNA variants via TCF1. This CLU transcript is shorter at the 5' end than reported by the RefSeq database, and produces the intracellular 60 kDa CLU protein isoform which is secreted as a ~80 kDa protein after post-translational processing.

Regulation of clusterin/apolipoprotein J, a functional homologue to the small heat shock proteins, by oxidative stress in ageing and age-related diseases

Clusterin/apolipoprotein J (CLU) gene has a nearly ubiquitous expression pattern in human tissues. The two main CLU protein isoforms in human cells include the conventional glycosylated secreted heterodimer (sCLU) and a truncated nuclear form (nCLU). CLU has been implicated in various physiological processes and in many severe physiological disturbance states including ageing, cancer progression, vascular damage, diabetes, kidney and neuron degeneration. Although unrelated in their etiology and clinical manifestation, these diseases represent states of increased oxidative stress, which in turn, promotes amorphous aggregation of target proteins, increased genomic instability and high rates of cellular death. Among the various properties attributed to CLU so far, those mostly investigated and invariably appreciated are its small heat shock proteins-like chaperone activity and its involvement in cell death regulation, which are both directly correlated to the main features of oxidant injury. Moreover, the presence of both a heat shock transcription factor-1 and an activator protein-1 element in the CLU gene promoter indicate that CLU gene can be an extremely sensitive biosensor to reactive oxygen species. This review emphasizes on CLU gene regulation by oxidative stress that is the common link between all pathological conditions where CLU has been implicated.

Characterization and functional consequences of underexpression of clusterin in rheumatoid arthritis

We previously compared by microarray analysis gene expression in rheumatoid arthritis (RA) and osteoarthritis (OA) tissues. Among the set of genes identified as a molecular signature of RA, clusterin (clu) was one of the most differentially expressed. In the present study we sought to assess the expression and the role of CLU (mRNA and protein) in the affected joints and in cultured fibroblast-like synoviocytes (FLS) and to determine its functional role. Quantitative RT-PCR, Northern blot, in situ hybridization, immunohistochemistry, and Western blot were used to specify and quantify the expression of CLU in ex vivo synovial tissue. In synovial tissue, the protein was predominantly expressed by synoviocytes and it was detected in synovial fluids. Both full-length and spliced isoform CLU mRNA levels of expression were lower in RA tissues compared with OA and healthy synovium. In synovium and in cultured FLS, the overexpression of CLU concerned all protein isoforms in OA whereas in RA, the intracellular forms of the protein were barely detectable. Transgenic overexpression of CLU in RA FLS promoted apoptosis within 24 h. We observed that CLU knockdown with small interfering RNA promoted IL-6 and IL-8 production. CLU interacted with phosphorylated IkappaBalpha. Differential expression of CLU by OA and RA FLS appeared to be an intrinsic property of the cells. Expression of intracellular isoforms of CLU is differentially regulated between OA and RA. We propose that in RA joints, high levels of extracellular CLU and low expression of intracellular CLU may enhance NF-kappaB activation and survival of the synoviocytes.

Global gene expression analysis in fetal mouse ovaries with and without meiosis and comparison of selected genes with meiosis in the testis

In order to identify novel genes involved in early meiosis and early ovarian development in the mouse, we used microarray technology to compare transcriptional activity in ovaries without meiotic germ cells at embryonic age 11.5 (E11.5) and E13.5 ovaries with meiosis. Overall, 182 genes were differentially expressed; 134 were known genes and 48 were functionally uncharacterized. A comparison of our data with the literature associated, for the first time, at least eight of the known genes with female meiosis/germ cell differentiation (Aldh1a1, C2pa, Tex12, Stk31, Lig3, Id4, Recql, Piwil2). These genes had previously only been described in spermatogenesis. The microarray also detected an abundance of vesicle-related genes of which four were upregulated (Syngr2, Stxbp1, Ric-8, SytIX) and one (Myo1c) was downregulated in E13.5 ovaries. Detailed analysis showed that the temporal expression of SytIX also coincided with the first meiotic wave in the pubertal testis. This is the first time that SytIX has been reported in non-neuronal tissue. Finally, we examined the expression of one of the uncharacterized genes and found it to be gonad-specific in adulthood. We named this novel transcript "Gonad-expressed transcript 1" (Get-1). In situ hybridization showed that Get-1 was expressed in meiotic germ cells in both fetal ovaries and mature testis. Get-1 is therefore a novel gene in both male and female meiosis.

Clusterin induces differentiation of pancreatic duct cells into insulin-secreting cells

AIMS/HYPOTHESIS

We recently reported that expression of the gene encoding clusterin (Clu) is upregulated in the regenerating pancreas, particularly in tissues undergoing differentiation. This led us to propose that clusterin participates in the cytodifferentiation of pancreatic tissue, particularly the endocrine islet cells. The aim of this study was to investigate whether clusterin induces the differentiation of duct-lining cells into insulin-secreting cells.

METHODS

We isolated ductal tissue from rat pancreas and cultured it to develop epithelial cell explants for transfection of the Clu cDNA as well as for treatment of clusterin protein.

RESULTS

The number of newly differentiated insulin cells increased 6.9-fold upon Clu overexpression compared with controls. Ins1 mRNA and peptide levels were also increased. Furthermore, glucose-stimulated insulin secretion was observed in the differentiated insulin cells. These cells were immunoreactive for insulin and C-peptide, but negative for other islet hormones and for cytokeratin-20, which indicates a fully differentiated state. Insulin cell differentiation was also increased in a dose-dependent manner by treating duct cells in culture with clusterin, indicating a growth-factor-like action of clusterin in insulin cell differentiation.

CONCLUSIONS/INTERPRETATION

These results suggest that clusterin can be considered as a potential morphogenic factor that promotes differentiation of pancreatic beta cells.

Stage-specific changes in gene expression in acutely isolated mouse CNS progenitor cells

Neural progenitor cells can be derived from a variety of developmental stages when they are preferentially proliferating, undergoing neurogenesis or undergoing gliogenesis. We used FACS sorting and the LeX surface marker to enrich neural progenitor cells from different embryonic stages and adult and compared their gene expression profiles using Affymetrix Microarrays. Our results show that, while there are common genes expressed in the progenitor cell population from all stages, there are also significant differences in gene expression patterns that correlate with stage-related behaviors. These data indicate that progenitor cells change during development and that adult and embryonic neural progenitor cells are intrinsically different.

Parasite interaction with host complement: beyond attack regulation

Many orthologous proteins of known mammalian receptors have been discovered in parasites. Besides disguising the parasite as self in terms of the host immune system, evidence is accumulating that these receptors link to signalling pathways in parasites that appear to be involved in their growth or development. Recently, several proteins of the host complement system, which forms part of the innate defence against invading microorganisms, have been shown to possess alternative functions. These complement proteins interact with signalling pathways involved in early development and differentiation, as well as organ and tissue regeneration. By altering cellular interactions and responses, complement is being shown to have novel roles besides the originally described inflammatory role. The possibility exists that, as for other host factors interacting with parasites and affecting their growth or development, host complement proteins could also have such an influence.

Myc-transformed epithelial cells down-regulate clusterin, which inhibits their growth in vitro and carcinogenesis in vivo

Effective treatment of malignant carcinomas requires identification of proteins regulating epithelial cell proliferation. To this end, we compared gene expression profiles in murine colonocytes and their c-Myc-transformed counterparts, which possess enhanced proliferative potential. A surprisingly short list of deregulated genes included the cDNA for clusterin, an extracellular glycoprotein without a firmly established function. We had previously demonstrated that in organs such as skin, clusterin expression is restricted to differentiating but not proliferating cell layers, suggesting a possible negative role in cell division. Indeed, its transient overexpression in Myc-transduced colonocytes decreased cell accumulation. Furthermore, clusterin was down-regulated in rapidly dividing human keratinocytes infected with a Myc-encoding adenovirus. Its knockdown via antisense RNA in neoplastic epidermoid cells enhanced proliferation. Finally, recombinant human clusterin suppressed, in a dose-dependent manner, DNA replication in keratinocytes and other cells of epithelial origin. Thus, clusterin appears to be an inhibitor of epithelial cell proliferation in vitro. To determine whether it also affects neoplastic growth in vivo, we compared wild-type and clusterin-null mice with respect to their sensitivity to 7, 12-dimethylbenz(a)anthracene /12-Otetradecanoylphorbol-13-acetate (DMBA/TPA)-induced skin carcinogenesis. We observed that the mean number of papillomas/mouse was higher in clusterin-null animals. Moreover, these papillomas did not regress as readily as in wild-type mice and persisted beyond week 35. The rate of progression toward squamous cell carcinoma was not altered, although those developing in clusterin-null mice were on average better differentiated. These data suggest that clusterin not only suppresses epithelial cell proliferation in vitro but also interferes with the promotion stage of skin carcinogenesis.

Structural characterization of native mouse zona pellucida proteins using mass spectrometry

The zona pellucida is an extracellular matrix consisting of three glycoproteins that surrounds mammalian eggs and mediates fertilization. The primary structures of mouse ZP1, ZP2, and ZP3 have been deduced from cDNA. Each has a predicted signal peptide and a transmembrane domain from which an ectodomain must be released. All three zona proteins undergo extensive co- and post-translational modifications important for secretion and assembly of the zona matrix. In this report, native zonae pellucidae were isolated and structural features of individual zona proteins within the mixture were determined by high resolution electrospray mass spectrometry. Complete coverage of the primary structure of native ZP3, 96% of ZP2, and 56% of ZP1, the least abundant zona protein, was obtained. Partial disulfide bond assignments were made for each zona protein, and the size of the processed, native protein was determined. The N termini of ZP1 and ZP3, but not ZP2, were blocked by cyclization of glutamine to pyroglutamate. The C termini of ZP1, ZP2, and ZP3 lie upstream of a dibasic motif, which is part of, but distinct from, a proprotein convertase cleavage site. The zona proteins are highly glycosylated and 4/4 potential N-linkage sites on ZP1, 6/6 on ZP2, and 5/6 on ZP3 are occupied. Potential O-linked carbohydrate sites are more ubiquitous, but less utilized.

Identification of a novel nuclear guanosine triphosphate-binding protein differentially expressed in renal disease

A novel guanosine triphosphate-binding protein, chronic renal failure gene (CRFG), was discovered by differential display PCR to be regulated differentially in renal disease. Within the rat kidney, CRFG mRNA was localized to the outer medulla and was highly expressed in epithelial cells. The specific renal expression of CRFG mRNA in the outer medulla was reduced dramatically in several rat models of renal disease, including diabetic nephropathy, partial nephrectomy, ischemia, and anti-Thy1.1-induced nephritis. CRFG was localized selectively in the nucleus of human and rodent cells, as determined by immunocytochemistry and green fluorescence fusion protein. Cellular mRNA levels of CRFG were also increased after serum administration, when cells proliferate. These data suggest that CRFG may be involved in regulating guanosine triphosphate-dependent nuclear events that are associated with cell proliferation and that are important in normal renal function and essential for growth and development.

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.

Clusterin regulates vascular smooth muscle cell nodule formation and migration

Vascular smooth muscle cells (VSMC) are the principal cellular component of the blood vessel wall where they exist in a differentiated state to maintain vascular tone. However, VSMC are not terminally differentiated and can be induced to dediffentiate, proliferate, and migrate. In fact, smooth muscle cell migration from the vascular wall into the lumen of the vessel is a central feature of occlusive vascular pathologies including atherosclerosis and intimal hyperplasia. In vitro, in the presence of an extracellular matrix, cultured vascular smooth muscle cells can migrate and invade the underlying gelatinous matrix, form multicellular nodular aggregations, and secrete the glycoprotein clusterin. Nodular cultures appear to mimic some of the properties of differentiated VSMC, in vivo. Here, to test the hypothesis that clusterin functions to modulate the formation of VSMC nodules and to facilitate cell migration a clusterin negative VSMC clone, SM-CLU13AS (Moulson and Millis, 1999, J Cell Physiol 180:355), was transiently transfected with plasmid pRcCMVCLU that contains the full-length porcine clusterin cDNA sequence under control of the CMV promoter. The transiently transfected VSMC culture expressed and secreted clusterin and formed nodules. To determine if clusterin regulates VSMC migration we used modified Boyden chamber assays. Clusterin, at 10 microg/ml, clearly promotes VSMC migration. In addition, a 15 amino acid synthetic peptide, representing amino acids 118-132 [KQTCMKFYARVCRSG] of the mature clusterin polypeptide, inhibits VSMC attachment to gelatinous substrate. Finally, clusterin appears to have a role in regulating endogenous clusterin expression in the clusterin negative clone. These results clearly establish that clusterin has functional role in VSMC nodule formation and support the conclusion that clusterin is a critical component of smooth muscle cell phenotypic modulation.

Clusterin gene transcription is activated by caudal-related homeobox genes in intestinal epithelium

Caudal-related homeobox (Cdx) proteins play an important role in development and differentiation of the intestinal epithelium. Using cDNA differential display, we identified clusterin as a prominently induced gene in a Cdx2-regulated cellular model of intestinal differentiation. Transfection experiments and DNA-protein interaction assays showed that clusterin is an immediate downstream target gene for Cdx proteins. The distribution of clusterin protein in the intestine was assessed during development and in the adult epithelium using immunohistochemistry. In the adult mouse epithelium, clusterin protein was localized in both crypt and villus compartments but not in interstitial cells of the intestinal mucosa. Together, these data suggest that clusterin is a direct target gene for Cdx homeobox proteins, and the pattern of clusterin protein expression suggests that it is associated with the differentiated state in the intestinal epithelium.

Apolipoprotein J (clusterin) and Alzheimer's disease

Apolipoprotein J (clusterin) is a ubiquitous multifunctional glycoprotein capable of interacting with a broad spectrum of molecules. In pathological conditions, it is an amyloid associated protein, co-localizing with fibrillar deposits in systemic and localized amyloid disorders. In Alzheimer's disease, the most frequent form of amyloidosis in humans and the major cause of dementia in the elderly, apoJ is present in amyloid plaques and cerebrovascular deposits but is rarely seen in NFT-containing neurons. ApoJ expression is up-regulated in a wide variety of insults and may represent a defense response against local damage to neurons. Four different mechanisms of action could be postulated to explain the role of apoJ as a neuroprotectant during cellular stress: (1) function as an anti-apoptotic signal, (2) protection against oxidative stress, (3) inhibition of the membrane attack complex of complement proteins locally activated as a result of inflammation, and (4) binding to hydrophobic regions of partially unfolded, stressed proteins, and therefore avoiding aggregation in a chaperone-like manner. This review focuses on the association of apoJ in biological fluids with Alzheimer's soluble Abeta. This interaction prevents Abeta aggregation and fibrillization and modulates its blood-brain barrier transport at the cerebrovascular endothelium.

Expression pattern of the epithelial v-like antigen (Eva) transcript suggests a possible role in placental morphogenesis

Adhesive mechanisms are considered to be of crucial importance for blastocyst adherence to the uterine wall, as well as for the interactions between embryonal and decidual tissues during hemochorial placenta formation. Epithelial V-like Antigen (Eva) is a novel homophilic adhesion molecule of the immunoglobulin superfamily, which during mouse embryonic development is expressed by various differentiating epithelia. In the present paper we describe Eva expression during mouse trophoblast invasion and placental morphogenesis, analysing day 5.5 to 18.5 postcoitum (p.c.) placentas and deciduomas by in situ hybridization. Eva transcripts were detected in spongiotrophoblast cells from 7.5 to 18.5 days p.c. Expression was uniform at early stages, but after day 11.5, p.c. became limited to the invasive subpopulation of spongiotrophoblasts (known as glycogen cells). Trophoblast giant cells did not express Eva in any of the stages analysed. Besides trophoblasts, also early postimplantation decidua was positive for Eva transcripts. In decidual tissue, Eva expression was present at day 5.5 p.c., peaked at day 7.5 p.c., and declined on successive days. The expression pattern of Eva transcripts suggests that during mouse placenta formation, its protein product may play a role in the processes of trophoblast invasion, decidual response, and trophoblast-decidual interaction.