J. Lipid Res.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Gander, R.
Right arrow Articles by Föger, B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Gander, R.
Right arrow Articles by Föger, B.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?
Journal of Lipid Research, Vol. 43, 636-645, April 2002
Copyright © 2002 by Lipid Research, Inc.

Molecular characterization of rabbit phospholipid transfer protein: choroid plexus and ependyma synthesize high levels of phospholipid transfer protein

Roland Gandera, Philipp Ellera, Susanne Kasera, Igor Theurla, Doris Walterb, Teresa Saupera, Andreas Ritscha, Josef R. Patscha, and Bernhard Fögera
a Department of Medicine, University of Innsbruck, Austria
b Department of Biochemical Pharmacology, University of Innsbruck, Austria

Correspondence to: Bernhard Föger, at the Department of Medicine, University of Innsbruck, Anichstrasse 35, A-6020 Austria., bernhard.foeger{at}uibk.ac.at (E-mail)


  ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALs AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES

Phospholipid transfer protein (PLTP) plays an important role in plasma lipoprotein metabolism. However, PLTP is expressed in a wide range of tissues suggesting additional local functions. To analyze the tissue distribution of PLTP in an animal with high-level expression of the structurally and functionally related CETP, we have cloned the full-length cDNA of rabbit PLTP (1,796 bp). Rabbit PLTP cDNA shows high homology to human, murine, and porcine PLTP cDNA, averaging 86.1%, 80.4%, and 86.1%, respectively. Interestingly, the C-terminus contains a unique seven amino acid insertion not found in previously characterized mammalian PLTPs. In clear contradistinction to human PLTP, rabbit PLTP mRNA was prominent in brain. In situ hybridization studies revealed specific, high-level synthesis of PLTP mRNA in choroid plexus and ependyma, the organs responsible for production of cerebrospinal fluid. Consistent with these findings, PLTP activity in cerebrospinal fluid amounted to 23% ± 3% of that in rabbit plasma. In contrast, neither CETP mRNA nor CETP activity were detectable in rabbit brain.

A role of PLTP in the central nervous system could involve some of its actions previously established in vitro, like proteolysis of apolipoproteins, and be physiologically relevant for neurodegenerative disorders such as Alzheimer's disease.—Gander, R., P. Eller, S. Kaser, I. Theurl, D. Walter, T. Sauper, A. Ritsch, J. R. Patsch, and B. Föger. Molecular characterization of rabbit phospholipid transfer protein: choroid plexus and ependyma synthesize high levels of phospholipid transfer protein. J. Lipid Res. 2002. 43: 636–645.

Supplementary key words: phospholipid transfer protein, rabbit, cDNA, choroid plexus, ependyma, cerebrospinal fluid


  INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALs AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES

At the outset of the present study, human (1), mouse (2), and pig (3) PLTP cDNA and human (4) and mouse (5) PLTP gene had already been identified. Nonetheless, we felt it would be worthwhile to clone and sequence the rabbit PLTP cDNA for basically three reasons.

First, PLTP is a member of the lipid transfer-lipopolysaccharide binding protein (LT-LBP) family comprised of, in addition to PLTP, CETP, bactericidal permeability increasing protein (BPI), and lipopolysaccharide binding protein (LBP). PLTP is essential for normal secretion (6) and lipolytic degradation of apolipoprotein B (apoB)-containing lipoproteins (7) (8) as well as for adequate lipidation (7) (8) and remodelling (9) (10) (11) of HDL. In the same vein, CETP is essential for intravascular remodelling of apoB-containing lipoproteins and HDL (12), leading to the appropriate speciation of LDL (13) and to generation of pre-ß HDL (14) (15). Thus, both lipid transfer proteins are structurally homologous (1) (12), are phospholipid transfer proteins (16), are HDL conversion factors (9) (10) (11) (17) (18), impact on both forward (12) and reverse (19) cholesterol transport, and have been demonstrated to interact both in vitro (16) and in vivo (20). In addition to PLTP, humans express CETP. Rabbits express even higher levels of CETP (21), whereas mice and pigs lack any appreciable amount of CETP expression. Given the close interrelationship between PLTP and CETP, rabbit data on PLTP regulation may therefore more closely mirror the human situation than data from mice or pigs.

Second, rabbits are well established models for atherosclerosis induced by a high cholesterol diet (22). Importantly, inhibition of CETP activity by specific CETP-antisense oligonucleotides (ODNs) (23), chemical compounds (24), and antibodies (25) leads to a substantial reduction of diet-induced atherosclerosis emphasizing the importance of lipid transfer proteins in atherogenesis. This is of special interest, as CETP overexpression in transgenic mice has proved to be pro-atherogenic in some models (26) (27), but clearly anti-atherogenic in others (28) (29). Thus, opposite conclusions regarding the atherogenic potential of a gene can result from studies in different metabolic contexts or animal models, as also nicely exemplified by models of LCAT overexpression (30). If so, specific inhibition of PLTP by antibodies, chemical inhibitors, or ODNs in the rabbit, which, like humans, expresses both PLTP and CETP, could likely be extrapolated to humans with a higher fidelity than rodent data.

Third, PLTP is expressed in a number of tissues not thought to be substantially involved in plasma lipoprotein transport, like pancreas, placenta, lung, gonads, and brain (2), suggesting a tissue-specific local function. Therapeutic manipulation of plasma lipid transfer proteins may inadvertently lead to side effects by compromising the local function of PLTP or CETP, i.e., by the use of inhibitors unable to discriminate between the LTPs (24). Thus, again, a detailed knowledge of PLTP expression in the rabbit may allow easier monitoring of potential adverse effects of inhibition of lipid transfer proteins in a model closely resembling the human situation.

Therefore, the rabbit model may provide unique insights into PLTP regulation and its effects on atherogenesis and may prove complementary to studies in mice overexpressing (11) (31) (32) (33) or lacking (6) (8) (20) (34) PLTP, which have greatly advanced our knowledge on this subject in the past 5 years. The present paper for the first time examines rabbit PLTP on a molecular level and reports the cloning and sequencing of the full-length rabbit PLTP cDNA, its functional expression in COS-7 cells, the tissue distribution of PLTP mRNA in nine different rabbit tissues, analysis of lipid transfer activities in rabbit cerebrospinal fluid and plasma, and a detailed characterization of brain regions synthesizing lipid transfer proteins by in situ hybridization studies.


  MATERIALs AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALs AND METHODS
RESULTS
 DISCUSSION
 REFERENCES

Samples
All samples were taken from Chinchilla Bastard rabbits aged between 5 and 15 months. Rabbits were housed at the Central Laboratory Animal Facilities in Innsbruck under protocols approved by the Austrian Animal Care and Use Comittee. Before taking blood, tissue, or cerebrospinal fluid samples, the rabbits were sacrificed by a 3-fold overdose of pentobarbital (Nembutal, Abbott Laboratories, Abbot Park, IL). Tissue samples for RNA isolation were frozen in liquid nitrogen until use. Cerebrospinal fluid was obtained by suboccipital puncture. Protein content of cerebrospinal fluid and plasma was determined according to Lowry et al. (35). Both were stored at -80°C. Rabbit brains were snap-frozen for 30 s in liquid-nitrogen-cooled 2-methylbutane immediately after removal and stored at -80°C until sections were performed.

RNA isolation and reverse transcription
Total RNA from rabbit tissues was prepared using a modified guanidinium isothiocyanate method (RNA-Clean, Dipro, Wiener Neustadt, Austria) and checked by photometric scanning and by agarose gel electrophoresis. Rabbit lung mRNA for rapid amplification of cDNA ends (RACE) was purchased from Clontech (Palo Alto, CA). The first strand cDNA synthesis of the rabbit lung mRNA was performed by using the AMV reverse transcription system from Clontech. The second strand was synthesized by a cocktail of Escherichia coli DNA polymerase I, E. coli DNA ligase, E. coli Rnase H, and T4 DNA Polymerase (Clontech).

cDNA cloning and PCR
Full length cDNA of rabbit PLTP was cloned in two steps. First a 645 bp fragment (175–819) of rabbit PLTP cDNA was amplified by PCR using redundant oligonucleotide primers deduced from the human and murine sequence (forward 645, reverse 645, MWGBiotech, Ebersberg, Germany), HotStarTaq polymerase (Qiagen, Germantown, MD) and doublestranded cDNA derived from rabbit lung mRNA as described above. After sequencing, new divergently directed primers were designed for RACE. The RACE procedure was carried out using the Marathon cDNA amplification kit (Clontech) according to the manufacturer's instructions.

Vector cloning
PCR products for sequencing were cloned into pCR2.1 vector (Invitrogen, Carlsbad, CA) by overhanging adenine residues produced by Taq polymerase. Complete rabbit PLTP cDNA was amplified by RT-PCR (forward rP, reverse rP, MWGBiotech, Ebersberg, Germany) using rabbit liver total RNA. Sequence analysis showed that using rabbit liver total RNA as a template for RT-PCR yields the same PLTP cDNA sequence as RACE-PCR from rabbit lung mRNA. In addition, we generated a hybrid cDNA comprising the complete rabbit PLTP cDNA and an additional 39 bp fragment (forward rPE = forward rP, reverse rPE, MWGBiotech) coding for an E-tag (Amersham Pharmacia Biotech, Uppsala, Sweden) in order to afford convenient immunological detection of the secreted fusion protein by specific antibodies to the E-tag. The E-tag forms the carboxy terminus of the fusion protein. The complete rabbit PLTP cDNA and the hybrid rabbit PLTP-E-tag cDNA were cloned into the pcDNA3.1 expression vector (Invitrogen, Carlsbad, CA) using HindIII restriction sites at the 5'-side and EcoRI and NotI at the 3'-side, respectively. The expression constructs contained an upstream CMV promotor and an SV-40 polyadenylation signal downstream of the expression cassette. The control plasmid [pcDNA3.1-green fluorescent protein (GFP)] contained the coding sequence of the GFP (36). All primers were designed with the help of the MacDNAsis V3.6 software (Hitachi Software Engineering, Berks, Great Britain). The expression plasmids were checked by sequencing.

Transient expression of rabbit PLTP and rabbit PLTP-E-tag in COS-7 cells
COS-7 cells (ATCC CRL-1651, Manassas, VA) were transfected by electroporation with 30 µg circular vector DNA (pcDNA3.1-rPLTP, pcDNA3.1-rPLTPE, or pcDNA3.1-GFP, respectively). PLTP and CETP activities were measured as previously described (37) (38) in samples of the cell-culture supernatants after 24 h, 48 h, 72 h, and 96 h and in the cell lysate after 96 h incubation. Transfer activities were corrected for cell-protein content measured by protein quantification (35). Culture supernatants of cells transfected with the rabbit PLTP-E-tag or the GFP construct were analyzed on 7.5% SDS-PAGE and blotted on hydrophobic polyvinylidene difluoride membranes (Amersham Pharmacia Biotech). Immunodetection of the recombinant rabbit PLTP-E-tag was carried out by using a monoclonal mouse anti E-tag antibody (Amersham Pharmacia Biotech). After immunodetection with a secondary, horseradish-peroxidase-conjugated goat anti mouse IgG antibody (Dako, Glostrup, Denmark) and chemoluminescent reaction using the electrochemiluminescence kit (ECL) Western blot reagent (Amersham Pharmacia Biotech) the blots were exposed to XAR films (Kodak, Vienna, Austria) and visualized by the Fluor-S-MultiImager (BioRad, Hercules, CA) using the Quantity One V1.1 software (BioRad).

In situ hybridization
Antisense PLTP or CETP oligonucleotides (PLinsitu A–D, CEinsitu A–D), designed to have a GC content of 40% to 60% and a length of 45 bp, were labeled with {alpha}32P dCTP (Code AA0075, Amersham Pharmacia Biotech) by the terminal deoxynucleotidyl transferase of calf thymus (Amersham Pharmacia Biotech) according to the manufacturer's instructions and diluted with hybridization buffer [4 x SSC, 5 x Denhardt's solultion, 200 µg/ml sheared salmon sperm DNA (Sigma Aldrich, St.Louis, MO, USA), 100 µg/ml long chain polyadenylic acid (Sigma Aldrich), 120 µg/ml heparin (Sigma Aldrich), 25 mM sodium phosphate, and 1 mM sodium pyrophosphate] to an activity of 5,000 cpm/µl. Frozen tissue samples were cut into 10 µm sections, fixed in 4% paraformaldehyde, submerged in 96% ethanol, and stored at 4°C until use. Labeled DNA probes were hybridized with the brain sections at 42°C for at least 12 h in a humified atmosphere. Subsequently, excess probe was removed by stringent washing for several times with 1 x SSC at 55°C followed by 50%, 75%, and 96% ethanol. Finally, sections were exposed to XAR films (Kodak) for 10 days. Control experiments were carried out by incubation of the brain sections with radiolabeled sense oligonucleotides. The sequences of the oligonucleotides can be obtained on request.

Statistics
Descriptive data are expressed as mean ± SD. Groups were compared by unpaired t-test. Statistical significance was inferred at a two-tailed P < 0.05 (SPSS for Windows 8.0).


  RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALs AND METHODS
 RESULTS
DISCUSSION
 REFERENCES

Cloning of full length rabbit PLTP cDNA
Full-length cDNA of rabbit PLTP was cloned in two steps. First, we amplified a 645 bp-part of rabbit PLTP cDNA by RT-PCR, using redundant primers based on the human and murine PLTP cDNA (1) (5) and subcloned it into the pCR2.1 vector. Subsequently, we designed new divergently-directed primers for the RACE procedure based on the sequence data of the rabbit PLTP cDNA fragment and obtained the complete rabbit PLTP cDNA (1,796 bp).

Analysis of rabbit PLTP cDNA
Our rabbit PLTP cDNA clone comprised 44 bp in 5'-direction of the putative translation start site, the entire coding region, and a 240 bp 3'-noncoding region including a poly(A)-tail (full length cDNA at the GenBank server, Accession Number AY072718). Rabbit PLTP cDNA contains an open reading frame of 1,512 bp predicting a protein of 503 amino acids. The coding cDNA region of rabbit PLTP shares an overall nucleotide identity of 86.1% with the human (1), 80.4% with the murine (2), and 86.1% with the porcine (3) cDNA, respectively. The deduced rabbit PLTP has 84.6% amino acid identity with human (1), 77.3% with murine (2), and 84.5% with porcine PLTP (3) ( Fig Table 1). As a largely conserved signal peptide of 17 amino acids is cleaved from the N-terminus of PLTP before its secretion (1), we predict the mature rabbit PLTP to comprise 486 amino acids. The calculated molecular mass of the mature rabbit PLTP is thus 53.4 kDa (Compute pI/Mw Tool, http://www.expasy.ch). The cystein residues at amino acid positions 5, 129, 168, and 318 of the secreted protein which are important for synthesis, secretion, and specific activity of PLTP (39) (40), are conserved in human, murine, porcine, and also in rabbit PLTP. Interestingly, the C-terminal region of rabbit PLTP shows a characteristic seven amino acid insertion (amino acids 477–483) which does not share with PLTP of any other species ( Fig Table 1). The three amino acid insertion (amino acids 488–490) at the C-terminus described by Pussinen et al. (3), for porcine is also present in rabbit PLTP but not in human or murine PLTP. The calculated isoelectric point (pI) of rabbit PLTP is 6.14. Murine PLTP has a pI of 6.19 while human, and in particular porcine, PLTP have much higher pIs according to the prediction model we used (Compute pI/Mw Tool). However, due to the conservative character of most substitutions, prediction of the secondary structures, O- and N-linked glycosylation sites (NetOGlyc 2.0, http://www.expasy.ch) revealed no major differences between rabbit PLTP and the PLTPs of other species.




View larger version (24K):
[in this window]
[in a new window]
  		Figure 1. Transient expression of rabbit phospholipid transfer protein (PLTP) in COS-7 cells. Phospholipid transfer activities after 24 h, 48 h, 72 h, and 96 h incubation. A: Time course of phospholipid transfer activities in cell culture supernatants of rabbit-PLTP-transfected COS-7 cells (closed diamond) and a control experiment with green fluorescent protein (GFP)-transfected COS-7 cells (closed square). B: Phospholipid transfer activity of rabbit-PLTP-E-tag-transfected COS-7 cells (closed diamond) and the GFP-control (closed square). Samples for both experiments were taken 24 h, 48 h, 72 h, and 96 h after transfection. Data are mean ± SD for three independent experiments and were corrected for protein content of cell lysates.




View larger version (33K):
[in this window]
[in a new window]
  		Figure 2. Transient expression of rabbit PLTP in COS-7 cells. Phospholipid transfer activities in cell culture supernatants (A) and cell lysates (B) after 96 h incubation. Data are mean ± SD for three independent experiments and were corrected for protein content of cell lysates.



View larger version (28K):
[in this window]
[in a new window]
  		Figure 3. Western blot analysis of recombinant rabbit PLTP. COS-7 cells were transfected with plasmids containing either recombinant rabbit PLTP-E-tag, native rabbit PLTP, or GFP using a monoclonal antibody against the E-tag contained in recombinant rabbit PLTP. Western blots of cell culture supernatants after 24, 48, 72, and 96 h (A–D) and lysates of COS-7 cells transfected with rabbit PLTP-E-tag after 96 h (lane H) showed a band corresponding to a molecular weight of approximately 75 kDa. Expectedly, no bands were detected in the cell culture supernatant of cells transfected with rabbit PLTP (F) or GFP (G) and the lysate of COS-7 cells transfected with GFP after 96 h incubation (I). Lane E shows a 30 kDa band corresponding to a E-tag positive control protein.



View larger version (15K):
[in this window]
[in a new window]
  		Figure 4. PLTP multiple tissue Northern blot. PLTP mRNA in nine different rabbit tissues normalized for ß-actin mRNA content. Data are mean ± SD for three independent experiments.




View larger version (25K):
[in this window]
[in a new window]
  		Figure 5. Phospholipid and cholesteryl ester transfer activities in rabbit cerebrospinal fluid and plasma. A: Phospholipid transfer activities of rabbit plasma (closed square) and rabbit cerebrospinal fluid (closed diamond). B: Cholesteryl ester transfer activities of different volumes of rabbit plasma (closed square) and rabbit cerebrospinal fluid (closed diamond). Data are mean ± SD for three independent experiments.



View larger version (43K):
[in this window]
[in a new window]
  		Figure 6. In situ detection of PLTP mRNA in rabbit brain. A and B show paramedian brain sections after hybridization with radiolabeled antisense PLTP oligonucleotides. The section showed at A has been exposed to a X-ray film for 8 days, the section at B for 11 days. D, E, G, and H show a sequence of frontal sections of the right brain hemisphere from cranial (D) to caudal (H) after hybridization with radiolabeled antisense PLTP oligonucleotides. C, F, and I show representative experiments with radiolabeled PLTP probes of sense polarity. The edges of the sections shown in C, F, and I are indicated by black linings. Arrows indicate specific neuro-anatomic structures: 1, choroid plexus and ependyma; 2, hippocampus; 3, corpus striatum; 4, lateral ventricle.



View larger version (104K):
[in this window]
[in a new window]
  		Figure 7. Table 1. Amino acid sequence alignment of PLTP from four species. PLTP sequences are shown in one-letter-code. Differences are highlighted white, the numbering is according to amino acid sequence. * Indicates in-frame stop codons.

Expression of functional rabbit PLTP in COS-7 cells
Expression constructs containing either just the rabbit PLTP coding region, rabbit PLTP cDNA including an additional carboxy-terminal E-tag sequence, or, as a positive control, the cDNA of GFP designed to allow convenient detection by specific antibodies, were transfected into COS-7 cells. After incubation for 24 h, 48 h, 72 h, and 96 h, samples from cells transfected with either rabbit PLTP cDNA ( Fig 1A) or rabbit PLTP cDNA with an added E-tag sequence (Fig 1b), facilitated radioactive phospholipid transfer, whereas supernatants from cells transfected with GFP cDNA did not (Fig 1a and Fig b). When compared with the amount of active PLTP present in the supernatants, trace amounts of active PLTP were found in cell lysates, indicating efficient secretion of both native rabbit PLTP and rabbit PLTP carrying an E-tag ( Fig 2A and B). Transfection of cells with the recombinant rabbit PLTP-E-tag allowed also immunodetection ( Fig 3) indicating an approximate molecular mass of 75 kDa. Thus, the calculated mass of rabbit PLTP (53.4 kDa) is substantially increased by glycosylation similar to PLTP isolated from human or porcine plasma.

Tissue specific expression of rabbit PLTP
PLTP mRNA tissue distribution was examined in three individual Chinchilla Bastard rabbits by Northern blots. The PLTP mRNA yielded a single band of 1.8 kb length and was normalized to the respective ß-actin mRNA. In all three rabbits, pancreatic tissue consistently expressed the highest amounts of PLTP mRNA followed by adipose tissue and the brain. Moderate levels were found in heart and liver tissues, whereas kidney, lung, and spleen yielded quite low levels. Skeletal muscle showed nearly no PLTP signal ( Fig 4). Our results are very similar to those of the pig which was investigated by a different quantitation method based on RT-PCR (3). Previous data of human and murine PLTP mRNA reported somewhat different expression patterns of PLTP (2). Interestingly, human PLTP mRNA in these reports was barely detectable in the brain.

Phospholipid transfer activity in rabbit plasma and cerebrospinal fluid
Protein content of plasma and cerebrospinal fluid averaged 55.5 ± 4 mg/ml and 0.412 ± 0.063 mg/ml, which falls within the normal range of reported rabbit values (41). Equal volumes of cerebrospinal fluid and plasma from three individual rabbits were pooled for one experiment because of the relatively low amount of cerebrospinal fluid that could be obtained from a single animal. Phospholipid transfer activity in cerebrospinal fluid was linear for sample volumes up to 125 µl ( Fig 5a). Phospholipid transfer activities detected in cerebrospinal fluid averaged approximately 23% of plasma values. Thus, normalized for protein content, disproportionately high amounts of active PLTP are present in rabbit cerebrospinal fluid.

Cholesteryl ester transfer activity in rabbit cerebrospinal fluid and plasma
Phospholipid transfer activities in the cerebrospinal fluid could simply be due to plasma PLTP transported into the cerebrospinal fluid via the blood-cerebrospinal-fluid barrier. If so, one would expect to also find another lipid transfer protein, CETP, which is also bound to HDL, in cerebrospinal fluid. CETP activity in plasma was linear up to 15 µl. However, no cholesteryl ester transfer could be detected in cerebrospinal fluid samples up to 50 µl (Fig 5b).

In situ hybridization of rabbit PLTP and CETP mRNA in brain sections
Paramedian sections of rabbit brain showed pronounced staining in the periventricular area, especially in the choroid plexus and the ependyma of the lateral ventricle ( Fig 6A and Fig B). After prolonged exposure we observed additional, more subtle differences, in PLTP expression among brain regions. Cortical white matter contained lower amounts of PLTP mRNA than corpus striatum and cortical gray matter (Fig 6B). Sequential frontal sections of the right brain hemisphere (Fig 6D, Fig E, Fig G, and Fig H) confirmed that choroid plexus and ependyma of the lateral ventricle were most strongly stained. In addition, corpus striatum showed relatively strong signals in the more cranial sections (Fig 6E).

The same set of experiments was also carried out with CETP probes which revealed no signals even after exposure for more than 10 days (data not shown). Negative control experiments revealed no detectable signal (Fig 6C, Fig F, and Fig I).


  DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALs AND METHODS
 RESULTS
 DISCUSSION
REFERENCES

This paper lays the basis for further studies examining PLTP regulation, its role in atherogenesis, and potential tissue-specific functions of PLTP in an animal with high level expression of the related CETP. Even from the present study, however, interesting findings have emerged both from analysis of rabbit PLTP structure and from a detailed characterization of its expression, especially in rabbit brain.

While rabbit PLTP shares a high overall homology with human (86.1%) (1), murine (5), and porcine (3) PLTP on a nucleic acid basis, two remarkable differences in amino acid sequence are nevertheless evident. As previously pointed out for porcine PLTP (3), an insertion of three amino acids at positions 488–490 is present in rabbit PLTP, which is not found in human and murine PLTP. A second insertion of seven amino acids at positions 477–483 is actually unique for rabbit PLTP. Whether or not the above or other changes in primary structure alter any of the multiple molecular functions of PLTP in the rabbit remains to be determined. However, studies on site-directed mutagenesis show that C-terminal deletion variants of 20 amino acids have specific activities of only approximately 30% compared with wild-type human PLTP (40). Thus, relatively subtle modification of the amino acid sequence of the C-terminus, as present in rabbit PLTP, may change function and/or substrate binding of PLTP.

PLTP and CETP are synthesized both in tissues with a major role in lipoprotein metabolism (1) (3) (5) (42) (43) (44) (45) (46), like liver and adipose, and in those without (1) (3) (5) (42) (43) (44) (45) (46), like pancreas and spleen. If there were a major overlap in physiological function between CETP and PLTP, one might expect to see a broader tissue pattern of PLTP expression in animals lacking CETP, like mouse and pig, than in the rabbit, which highly expresses both lipid transfer proteins. PLTP expression in the rabbit in this study, however, fails to confirm this expectation and is actually very similar to the tissue pattern of murine (2) and porcine (3) PLTP with high levels of PLTP mRNA in pancreas, placenta, lung, brain, adipose, liver, and heart and lower levels in skeletal muscle, spleen, and kidney. The similar tissue pattern confirms the concept that PLTP and CETP have specialized non-overlapping functions in vivo (20) and extends its validity from plasma lipoprotein metabolism to the cellular level.

Interestingly, brain ranks second in PLTP mRNA content in both mouse (2) and pig (3), and third in the rabbit (Fig 4). In contrast, PLTP mRNA content in human brain consistently ranks last of all tissues examined (1) (2). Thus, brain is the only tissue with a major species-specific variation in PLTP expression identified so far. Generally, tissue-specific expression of PLTP seems to be more conserved than that of CETP, where some species completely lack CETP (21) and others fail to express CETP in critical organs like the liver (45). Taken together, tight preservation of tissue-specific expression of PLTP and regulation by local factors (47) strongly suggest important local functions of PLTP.

A high content of PLTP mRNA in rabbit brain does not necessarily imply that bioactive PLTP is actually secreted by this tissue. We therefore quantified PLTP-activity in cerebrospinal fluid and found that it amounted to roughly 23% of the plasma activity on a v/v basis (Fig 5). Given the fact that the protein content of normal rabbit cerebrospinal fluid is approximately two orders of magnitude lower than that of plasma (41) and assuming a normal specific activity of PLTP in cerebrospinal fluid, we estimate the relative PLTP concentration of rabbit cere-brospinal fluid to exceed that of plasma by at least 20-fold. If the cerebrospinal fluid, like plasma (48), were to contain both active and inactive forms of PLTP, extrapolation from activity to PLTP mass data would be further complicated. Even the relatively high PLTP activity in the cerebrospinal fluid need not be due necessarily to local PLTP synthesis, but could reflect efficient active transport from plasma. In order to further explore the possibility that PLTP activity in cerebrospinal fluid derives from plasma, we determined the activity of CETP in cerebrospinal fluid. As both the literature (42) (43) (44) (45) (46) and our own data in the rabbit show that brain lacks CETP mRNA, the only conceivable source of CETP in cerebrospinal fluid would be transport from plasma. CETP shares close structural homology with PLTP (12) (49) and is transported in plasma bound to a similar subset of HDL particles (37) making a selective transport of PLTP, but not CETP, quite unlikely. Expectedly, we found substantial CETP activity in rabbit plasma, but, interestingly, none in rabbit cerebrospinal fluid (Fig 5), strengthening the notion that PLTP is indeed synthesized locally within the central nervous system (CNS). Even in humans, with clearly lower levels of PLTP mRNA in the CNS, recently PLTP activity and mass was shown to be present in cerebrospinal fluid (50), averaging about 1% of plasma values. This seemingly low level of activity should be seen in the context of cerebrospinal fluid lipid and apoA-I (51) concentrations, which also average about 1% of plasma levels, indicating that PLTP activity, even in humans, clearly has the potential to substantially modulate the metabolism of lipoproteins in cerebrospinal fluid.

Brain comprises various neuroanatomic structures with differing functions. Thus, we were interested if secretion of PLTP was a global property of all brain structures or specific for some regions. In situ hybridization experiments demonstrated choroid plexus and ependyma to be by far the most prominently stained structures (Fig 6). Choroid plexus and ependyma have evolved to produce and resorb the cerebrospinal fluid filling ventricles, a compartment turning over four to five times each day (52). In hindsight, high level secretion of PLTP by the plexus should not have been a surprise, as PLTP is prominently expressed in endothelial cells and was actually first cloned from a human endothelial cDNA library (1). However, coordinated high-level expression of PLTP both in endothelial cells of the choroid plexus and in epithelial cells of the adjacent ependyma very strongly supports a functional role of PLTP in the cerebrospinal fluid.

In addition to the prominent expression of PLTP in choroid plexus and ependyma, PLTP expression was clearly detectable in corpus striatum and cortical gray matter, and at lower levels also in cortical white matter. On the other hand, the lack of CETP activity in the cerebrospinal fluid and the completely negative results of the in situ hybridization with CETP-antisense probes clearly show the lack of functional overlap between the two transfer proteins in rabbit brain. This observation is of some interest, as CETP activity has been reported to be detectable in human brain (53).

Recently, a growing body of evidence supports an important role of cerebrospinal fluid lipoproteins in the transport of essential fatty acids, lipid-soluble vitamins, cholesterol, and also in the removal of oxysterols formed by degenerative processes (51). A number of components of the lipid transport system in cerebrospinal fluid, such as some apolipoproteins (i.e., apoE, apoD, and apoJ), receptors (i.e., LDL-receptor, LRP, and megalin), and enzymes [i.e., LCAT (50)] are synthesized locally, others are imported from plasma [i.e., apoA-I (51) (54)]. Our data add PLTP to the roster of enzymes secreted by mammalian brain and detail its neuroanatomical localization. Functionally, PLTP might be involved in the proteolysis of apolipoproteins (55), in the remodeling of cerebrospinal fluid HDL, in the stimulation of cholesterol efflux from neuronal cells, or in the equilibration of vitamin E between lipoproteins and cells (56) (57). A specific down-regulation of PLTP in the central nervous system of patients with Down syndrome (58) is in line with a role of cerebrospinal fluid lipoproteins and PLTP in neurodegenerative disease. Which precise physiological role PLTP plays in the CNS remains speculative.

In conclusion, elucidation of the role of PLTP in cholesterol and phospholipid homeostasis in vasculature and brain may provide important clues for the prevention and treatment of atherosclerosis and neurodegenerative diseases, i.e., Alzheimer's disease. We hope that studies of PLTP function and regulation in the rabbit will significantly contribute to this promising area of investigation.


  ACKNOWLEDGMENTS

The authors thank Karin Salzmann (Department of Medicine, Innsbruck) and Willi Salvenmoser (Department of Zoology and Limnology, Innsbruck) for expert technical assistance, as well as Dr. Hermann Dietrich and Ernst Rainer (Central Laboratory Animal Facilities, Innsbruck) for their outstanding support in obtaining fresh samples from rabbits. This work was supported by a grant from the Jubiläumsfonds der Österreichischen Nationalbank (grant 8539 to B.F.), and a grant from the Fösterreichischer Fonds zur Förderung der wissenschaftlichen Forschung (grant 11693-MED to J.R.P.).

Manuscript received October 31, 2001; and in revised form January 25, 2002

Abbreviations: LTP, lipid transfer protein; ODN, oligonucleotide; PLTP, phospholipid transfer protein; SSC, sodium chloride-sodium citrate


  REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALs AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES

  1. Day, J. R., Albers, J. J., Lofton-Day, C. E., Gilbert, T. L., Ching, A. F., Grant, F. J., O'Hara, P. J., Marcovina, S. M., Adolphson, J. L. 1994. Complete cDNA encoding human phospholipid transfer protein from human endothelial cells. J. Biol. Chem. 269:9388-9391[Abstract/Free Full Text].

  2. Albers, J. J., Wolfbauer, G., Cheung, M. C., Day, J. R., Ching, A. F., Lok, S., Tu, A. Y. 1995. Functional expression of human and mouse plasma phospholipid transfer protein: effect of recombinant and plasma PLTP on HDL subspecies. Biochim. Biophys. Acta. 1258:27-34[Medline].

  3. Pussinen, P. J., Olkkonen, V. M., Jauhiainen, M., Ehnholm, C. 1997. Molecular cloning and functional expression of cDNA encoding the pig plasma phospholipid transfer protein. J. Lipid Res. 38:1473-1481[Abstract].

  4. Tu, A. Y., Wolfbauer, G., Albers, J. J. 1995. Functional characterization of the promoter region of the human phospholipid transfer protein gene. Biochem. Biophys. Res. Commun. 217:705-711[CrossRef][Medline].

  5. Tu, A. Y., Chen, H., Johnson, K. A., Paigen, B., Albers, J. J. 1997. Characterization of the mouse gene encoding phospholipid transfer protein. Gene. 188:115-118[CrossRef][Medline].

  6. Jiang, X. C., Qin, S., Qiao, C., Kawano, K., Lin, M., Skold, A., Xiao, X., Tall, A. R. 2001. Apolipoprotein B secretion and atherosclerosis are decreased in mice with phospholipid-transfer protein deficiency. Nat. Med 7:847-852[CrossRef][Medline].

  7. Tall, A. R., Krumholz, S., Olivecrona, T., Deckelbaum, R. J. 1985. Plasma phospholipid transfer protein enhances transfer and exchange of phospholipids between very low density lipoproteins and high density lipoproteins during lipolysis. J. Lipid Res. 26:842-851[Abstract].

  8. Jiang, X. C., Bruce, C., Mar, J., Lin, M., Ji, Y., Francone, O. L., Tall, A. R. 1999. Targeted mutation of plasma phospholipid transfer protein gene markedly reduces high-density lipoprotein levels. J. Clin. Invest 103:907-914[Medline].

  9. Jauhiainen, M., Metso, J., Pahlman, R., Blomqvist, S., van Tol, A., Ehnholm, C. 1993. Human plasma phospholipid transfer protein causes high density lipoprotein conversion. J. Biol. Chem. 268:4032-4036[Abstract/Free Full Text].

  10. Tu, A. Y., Nishida, H. I., Nishida, T. 1993. High density lipoprotein conversion mediated by human plasma phospholipid transfer protein. J. Biol. Chem. 268:23098-23105[Abstract/Free Full Text].

  11. Foger, B., Santamarina-Fojo, S., Shamburek, R. D., Parrot, C. L., Talley, G. D., Brewer, H. B., Jr. 1997. Plasma phospholipid transfer protein. Adenovirus-mediated overexpression in mice leads to decreased plasma high density lipoprotein (HDL) and enhanced hepatic uptake of phospholipids and cholesteryl esters from HDL. J. Biol. Chem. 272:27393-27400[Abstract/Free Full Text].

  12. Tall, A. 1995. Plasma lipid transfer proteins. Annu. Rev. Biochem. 64:235-257[CrossRef][Medline].

  13. Sakai, N., Matsuzawa, Y., Hirano, K., Yamashita, S., Nozaki, S., Ueyama, Y., Kubo, M., Tarui, S. 1991. Detection of two species of low density lipoprotein particles in cholesteryl ester transfer protein deficiency. Arterioscler. Thromb. 11:71-79[Abstract/Free Full Text].

  14. Barter, P. J., Chang, L. B., Newnham, H. H., Rye, K. A., Rajaram, O. V. 1990. The interaction of cholesteryl ester transfer protein and unesterified fatty acids promotes a reduction in the particle size of high-density lipoproteins. Biochim. Biophys. Acta. 1045:81-89[Medline].

  15. Lagrost, L., Florentin, E., Guyard-Dangremont, V., Athias, A., Gandjini, H., Lallemant, C., Gambert, P. 1995. Evidence for nonesterified fatty acids as modulators of neutral lipid transfers in normolipidemic human plasma. Arterioscler. Thromb. Vasc. Biol. 15:1388-1396[Abstract/Free Full Text].

  16. Lagrost, L., Athias, A., Gambert, P., Lallemant, C. 1994. Comparative study of phospholipid transfer activities mediated by cholesteryl ester transfer protein and phospholipid transfer protein. J. Lipid Res. 35:825-835[Abstract].

  17. Rye, K. A., Garrety, K. H., Barter, P. J. 1992. Changes in the size of reconstituted high density lipoproteins during incubation with cholesteryl ester transfer protein: the role of apolipoproteins. J. Lipid Res. 33:215-224[Abstract].

  18. Lagrost, L., Gambert, P., Dangremont, V., Athias, A., Lallemant, C. 1990. Role of cholesteryl ester transfer protein (CETP) in the HDL conversion process as evidenced by using anti-CETP monoclonal antibodies. J. Lipid Res. 31:1569-1575[Abstract].

  19. Patsch, J. R., and A. M. Gotto. 1987. Metabolism of high density lipoproteins. In Plasma Lipoproteins. A. M. Gotto, Jr., editor. Elsevier, Amsterdam. 221–259.

  20. Kawano, K., Qin, S. C., Lin, M., Tall, A. R., Jiang, X. C. 2000. Cholesteryl ester transfer protein and phospholipid transfer protein have nonoverlapping functions in vivo. J. Biol. Chem 275:29477-29481[Abstract/Free Full Text].

  21. Ha, Y. C., Barter, P. J. 1982. Differences in plasma cholesteryl ester transfer activity in sixteen vertebrate species. Comp. Biochem. Physiol. B. 71:265-269[CrossRef][Medline].

  22. Kolodgie, F. D., Katocs, A. S., Jr., Largis, E. E., Wrenn, S. M., Cornhill, J. F., Herderick, E. E., Lee, S. J., Virmani, R. 1996. Hypercholesterolemia in the rabbit induced by feeding graded amounts of low-level cholesterol. Methodological considerations regarding individual variability in response to dietary cholesterol and development of lesion type. Arterioscler. Thromb. Vasc. Biol. 16:1454-1464[Abstract/Free Full Text].

  23. Sugano, M., Makino, N., Sawada, S., Otsuka, S., Watanabe, M., Okamoto, H., Kamada, M., Mizushima, A. 1998. Effect of antisense oligonucleotides against cholesteryl ester transfer protein on the development of atherosclerosis in cholesterol-fed rabbits. J. Biol. Chem. 273:5033-5036[Abstract/Free Full Text].

  24. Okamoto, H., Yonemori, F., Wakitani, K., Minowa, T., Maeda, K., Shinkai, H. 2000. A cholesteryl ester transfer protein inhibitor attenuates atherosclerosis in rabbits. Nature. 406:203-207[CrossRef][Medline].

  25. Rittershaus, C. W., Miller, D. P., Thomas, L. J., Picard, M. D., Honan, C. M., Emmett, C. D., Pettey, C. L., Adari, H., Hammond, R. A., Beattie, D. T., Callow, A. D., Marsh, H. C., U. S. Ryan,. 2000. Vaccine-induced antibodies inhibit CETP activity in vivo and reduce aortic lesions in a rabbit model of atherosclerosis. Arterioscler. Thromb. Vasc. Biol 20:2106-2112[Abstract/Free Full Text].

  26. Marotti, K. R., Castle, C. K., Boyle, T. P., Lin, A. H., Murray, R. W., Melchior, G. W. 1993. Severe atherosclerosis in transgenic mice expressing simian cholesteryl ester transfer protein. Nature 364:73-75[CrossRef][Medline].

  27. Plump, A. S., Masucci-Magoulas, L., Bruce, C., Bisgaier, C. L., Breslow, J. L., Tall, A. R. 1999. Increased atherosclerosis in ApoE and LDL receptor gene knock-out mice as a result of human cholesteryl ester transfer protein transgene expression. Arterioscler. Thromb. Vasc. Biol. 19:1105-1110[Abstract/Free Full Text].

  28. Hayek, T., Masucci-Magoulas, L., Jiang, X., Walsh, A., Rubin, E., Breslow, J. L., Tall, A. R. 1995. Decreased early atherosclerotic lesions in hypertriglyceridemic mice expressing cholesteryl ester transfer protein transgene. J. Clin. Invest. 96:2071-2074.

  29. Foger, B., Chase, M., Amar, M. J., Vaisman, B. L., Shamburek, R. D., Paigen, B., Fruchart-Najib, J., Paiz, J. A., Koch, C. A., Hoyt, R. F., Brewer, H. B., Jr., Santamarina-Fojo, S. 1999. Cholesteryl ester transfer protein corrects dysfunctional high density lipoproteins and reduces aortic atherosclerosis in lecithin cholesterol acyltransferase transgenic mice. J. Biol. Chem. 274:36912-36920[Abstract/Free Full Text].

  30. Santamarina-Fojo, S., Lambert, G., Hoeg, J. M., Brewer, H. B., Jr. 2000. Lecithin-cholesterol acyltransferase: role in lipoprotein metabolism, reverse cholesterol transport and atherosclerosis. Curr. Opin. Lipidol. 11:267-275[CrossRef][Medline].

  31. Jiang, X., Francone, O. L., Bruce, C., Milne, R., Mar, J., Walsh, A., Breslow, J. L., Tall, A. R. 1996. Increased prebeta-high density lipoprotein, apolipoprotein AI, and phospholipid in mice expressing the human phospholipid transfer protein and human apolipoprotein AI transgenes. J. Clin. Invest. 98:2373-2380[Medline].

  32. Ehnholm, S., van Dijk, K. W., van ‘t Hof, B., van der Zee, A., Olkkonen, V. M., Jauhiainen, M., Hofker, M., Havekes, L., Ehnholm, C. 1998. Adenovirus mediated overexpression of human phospholipid transfer protein alters plasma HDL levels in mice. J. Lipid Res 39:1248-1253[Abstract/Free Full Text].

  33. van Haperen, R., van Tol, A., Vermeulen, P., Jauhiainen, M., van Gent, T., van den Berg, P., Ehnholm, S., Grosveld, F., van der Kamp, A., de Crom, R. 2000. Human plasma phospholipid transfer protein increases the antiatherogenic potential of high density lipoproteins in transgenic mice. Arterioscler. Thromb. Vasc. Biol. 20:1082-1088[Abstract/Free Full Text].

  34. Qin, S., Kawano, K., Bruce, C., Lin, M., Bisgaier, C., Tall, A. R., Jiang, X. 2000. Phospholipid transfer protein gene knock-out mice have low high density lipoprotein levels, due to hypercatabolism, and accumulate apoA-IV-rich lamellar lipoproteins. J. Lipid Res 41:269-276[Abstract/Free Full Text].

  35. Lowry, O. H., Rosebrough, N. J., Farr, A. I., Randall, R. J. 1951. Protein measurement with the Folin phenol reagent. J. Biol. Chem. 192:265-270.

  36. Prendergast, F. G. 1999. Biophysics of the green fluorescent protein. Methods Cell Biol. 58:1-18[Medline].

  37. Speijer, H., Groener, J. E., van Ramshorst, E., van Tol, A. 1991. Different locations of cholesteryl ester transfer protein and phospholipid transfer protein activities in plasma. Atherosclerosis. 90:159-168[CrossRef][Medline].

  38. Groener, J. E., Pelton, R. W., Kostner, G. M. 1986. Improved estimation of cholesteryl ester transfer/exchange activity in serum or plasma. Clin. Chem. 32:283-286[Abstract/Free Full Text].

  39. Qu, S. J., Fan, H. Z., Kilinc, C., Pownall, H. J. 1999. Role of cysteine residues in human plasma phospholipid transfer protein. J. Protein Chem. 18:193-198[CrossRef][Medline].

  40. Huuskonen, J., Wohlfahrt, G., Jauhiainen, M., Ehnholm, C., Teleman, O., Olkkonen, V. M. 1999. Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis. J. Lipid Res. 40:1123-1130[Abstract/Free Full Text].

  41. Kusumi, R. K., Plouffe, J. F. 1980. Cerebrospinal fluid glucose and protein values in normal rabbits. Lab. Anim. 14:41-42[Abstract/Free Full Text].

  42. Nagashima, M., McLean, J. W., Lawn, R. M. 1988. Cloning and mRNA tissue distribution of rabbit cholesteryl ester transfer protein. J. Lipid Res. 29:1643-1649[Abstract].

  43. Pape, M. E., Rehberg, E. F., Marotti, K. R., Melchior, G. W. 1991. Molecular cloning, sequence, and expression of cynomolgus monkey cholesteryl ester transfer protein. Inverse correlation between hepatic cholesteryl ester transfer protein mRNA levels and plasma high density lipoprotein levels. Arterioscler. Thromb. 11:1759-1771[Abstract/Free Full Text].

  44. Pape, M. E., Ulrich, R. G., Rea, T. J., Marotti, K. R., Melchior, G. W. 1991. Evidence that the nonparenchymal cells of the liver are the principal source of cholesteryl ester transfer protein in primates. J. Biol. Chem. 266:12829-12831[Abstract/Free Full Text].

  45. Jiang, X. C., Moulin, P., Quinet, E., Goldberg, I. J., Yacoub, L. K., Agellon, L. B., Compton, D., Schnitzer-Polokoff, R., Tall, A. R. 1991. Mammalian adipose tissue and muscle are major sources of lipid transfer protein mRNA. J. Biol. Chem. 266:4631-4639[Abstract/Free Full Text].

  46. Drayna, D., Jarnagin, A. S., McLean, J., Henzel, W., Kohr, W., Fielding, C., Lawn, R. 1987. Cloning and sequencing of human cholesteryl ester transfer protein cDNA. Nature. 327:632-634[CrossRef][Medline].

  47. Jiang, X. C., D'Armiento, J., Mallampalli, R. K., Mar, J., Yan, S. F., Lin, M. 1998. Expression of plasma phospholipid transfer protein mRNA in normal and emphysematous lungs and regulation by hypoxia. J. Biol. Chem 273:15714-15718[Abstract/Free Full Text].

  48. Oka, T., Kujiraoka, T., Ito, M., Egashira, T., Takahashi, S., Nanjee, M. N., Miller, N. E., Metso, J., Olkkonen, V. M., Ehnholm, C., Jauhiainen, M., Hattori, H. 2000. Distribution of phospholipid transfer protein in human plasma: presence of two forms of phospholipid transfer protein, one catalytically active and the other inactive. J. Lipid Res. 41:1651-1657[Abstract/Free Full Text].

  49. Hubacek, J. A., Buchler, C., Aslanidis, C., Schmitz, G. 1997. The genomic organization of the genes for human lipopolysaccharide binding protein (LBP) and bactericidal permeability increasing protein (BPI) is highly conserved. Biochem. Biophys. Res. Commun. 236:427-430[CrossRef][Medline].

  50. Demeester, N., Castro, G., Desrumaux, C., De Geitere, C., Fruchart, J. C., Santens, P., Mulleners, E., Engelborghs, S., De Deyn, P. P., Vandekerckhove, J., Rosseneu, M., Labeur, C. 2000. Characterization and functional studies of lipoproteins, lipid transfer proteins, and lecithin:cholesterol acyltransferase in CSF of normal individuals and patients with Alzheimer's disease. J. Lipid Res. 41:963-974[Abstract/Free Full Text].

  51. Koch, S., and U. Beisiegel. 2000. Lipoproteins in the brain: a new frontier? In Lipids and Vascular Disease. J. D. Betteridge, editor. Martin Dunitz, London. 51–65.

  52. Adams, R. D., M. Victor, and A. Ropper. 1997. Disturbances of cerebrospinal fluid and its circulation, including hydrocephalus and meningeal reactions. In Principles of Neurology. M. J. Wonsiewicz, and M. Navrozov, editors. McGraw-Hill, New York. 623–641.

  53. Albers, J. J., Tollefson, J. H., Wolfbauer, G., Albright, R. E., Jr. 1992. Cholesteryl ester transfer protein in human brain. Int. J. Clin. Lab. Res. 21:264-266[Medline].

  54. Koch, S., Donarski, N., Goetze, K., Kreckel, M., Stuerenburg, H. J., Buhmann, C., Beisiegel, U. 2001. Characterization of four lipoprotein classes in human cerebrospinal fluid. J. Lipid Res. 42:1143-1151[Abstract/Free Full Text].

  55. Jauhiainen, M., Huuskonen, J., Baumann, M., Metso, J., Oka, T., Egashira, T., Hattori, H., Olkkonen, V. M., Ehnholm, C. 1999. Phospholipid transfer protein (PLTP) causes proteolytic cleavage of apolipoprotein A-I. J. Lipid Res. 40:654-664[Abstract/Free Full Text].

  56. Kostner, G. M., Oettl, K., Jauhiainen, M., Ehnholm, C., Esterbauer, H., Dieplinger, H. 1995. Human plasma phospholipid transfer protein accelerates exchange/transfer of alpha-tocopherol between lipoproteins and cells. Biochem. J. 305:659-667.

  57. Desrumaux, C., Deckert, V., Athias, A., Masson, D., Lizard, G., Palleau, V., Gambert, P., Lagrost, L. 1999. Plasma phospholipid transfer protein prevents vascular endothelium dysfunction by delivering alpha-tocopherol to endothelial cells. FASEB J. 13:883-892[Abstract/Free Full Text].

  58. Krapfenbauer, K., Yoo, B. C., Kim, S. H., Cairns, N., Lubec, G. 2001. Differential display reveals downregulation of the phospholipid transfer protein (PLTP) at the mRNA level in brains of patients with Down syndrome. Life Sci. 68:2169-2179[CrossRef][Medline].


Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati    What's this?


This article has been cited by other articles:


Home page
 DiabetesHome page
G. M. Dallinga-Thie, A. van Tol, H. Hattori, P. C.N. Rensen, E. J.G. Sijbrands, and for the Diabetes Atorvastatin Lipid Intervention (
Plasma phospholipid transfer protein activity is decreased in type 2 diabetes during treatment with atorvastatin: a role for apolipoprotein e?
Diabetes, May 1, 2006; 55(5): 1491 - 1496.
[Abstract] [Full Text] [PDF]

Home page
 J. Lipid Res.Home page
S. Vuletic, L.-W. Jin, S. M. Marcovina, E. R. Peskind, T. Moller, and J. J. Albers
Widespread distribution of PLTP in human CNS: evidence for PLTP synthesis by glia and neurons, and increased levels in Alzheimer's disease
J. Lipid Res., June 1, 2003; 44(6): 1113 - 1123.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Gander, R.
Right arrow Articles by Föger, B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Gander, R.
Right arrow Articles by Föger, B.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit