Cardiac glycoside-mediated turnover of Na, K-ATPases as a rational approach to reducing cell surface levels of the cellular prion protein

It is widely anticipated that a reduction of brain levels of the cellular prion protein (PrP^C) can prolong survival in a group of neurodegenerative diseases known as prion diseases. To date, efforts to decrease steady-state PrP^C levels by targeting this protein directly with small molecule drug-like compounds have largely been unsuccessful. Recently, we reported Na,K-ATPases to reside in immediate proximity to PrP^C in the brain, unlocking an opportunity for an indirect PrP^C targeting approach that capitalizes on the availability of potent cardiac glycosides (CGs). Here, we report that exposure of human co-cultures of neurons and astrocytes to non-toxic nanomolar levels of CGs causes profound reductions in PrP^C levels. The mechanism of action underpinning this outcome relies primarily on a subset of CGs engaging the ATP1A1 isoform, one of three α subunits of Na,K-ATPases expressed in brain cells. Upon CG docking to ATP1A1, the ligand receptor complex, and PrP^C along with it, is internalized by the cell. Subsequently, PrP^C is channeled to the lysosomal compartment where it is digested in a manner that can be rescued by silencing the cysteine protease cathepsin B. These data signify that the repurposing of CGs may be beneficial for the treatment of prion disorders.

The aminoglycoside G418 hinders de novo prion infection in cultured cells

The study of prions and the discovery of candidate therapeutics for prion disease have been facilitated by the ability of prions to replicate in cultured cells. Paradigms in which prion proteins from different species are expressed in cells with low or no expression of endogenous prion protein (PrP) have expanded the range of prion strains that can be propagated. In these systems, cells stably expressing a PrP of interest are typically generated via coexpression of a selectable marker and treatment with an antibiotic. Here, we report the unexpected discovery that the aminoglycoside G418 (Geneticin) interferes with the ability of stably transfected cultured cells to become infected with prions. In G418-resistant lines of N2a or CAD5 cells, the presence of G418 reduced levels of protease-resistant PrP following challenge with the RML or 22L strains of mouse prions. G418 also interfered with the infection of cells expressing hamster PrP with the 263K strain of hamster prions. Interestingly, G418 had minimal to no effect on protease-resistant PrP levels in cells with established prion infection, arguing that G418 selectively interferes with de novo prion infection. As G418 treatment had no discernible effect on cellular PrP levels or its localization, this suggests that G418 may specifically target prion assemblies or processes involved in the earliest stages of prion infection.

The IDIP framework for assessing protein function and its application to the prion protein

The quest to determine the function of a protein can represent a profound challenge. Although this task is the mandate of countless research groups, a general framework for how it can be approached is conspicuously lacking. Moreover, even expectations for when the function of a protein can be considered to be 'known' are not well defined. In this review, we begin by introducing concepts pertinent to the challenge of protein function assignments. We then propose a framework for inferring a protein's function from four data categories: 'inheritance', 'distribution', 'interactions' and 'phenotypes' (IDIP). We document that the functions of proteins emerge at the intersection of inferences drawn from these data categories and emphasise the benefit of considering them in an evolutionary context. We then apply this approach to the cellular prion protein (PrP^C ), well known for its central role in prion diseases, whose function continues to be considered elusive by many investigators. We document that available data converge on the conclusion that the function of the prion protein is to control a critical post-translational modification of the neural cell adhesion molecule in the context of epithelial-to-mesenchymal transition and related plasticity programmes. Finally, we argue that this proposed function of PrP^C has already passed the test of time and is concordant with the IDIP framework in a way that other functions considered for this protein fail to achieve. We anticipate that the IDIP framework and the concepts analysed herein will aid the investigation of other proteins whose primary functional assignments have thus far been intractable.

Cold Tolerance of the Tribolium castaneum (Coleoptera: Tenebrionidae), Under Different Thermal Regimes: Impact of Cold Acclimation

The red flour beetle, Tribolium castaneum (Herbst), is a serious pest of stored product worldwide. Cold tolerance or cold hardiness is an important ecophysiological trait related directly to survival, fitness, and distribution of insects. In this study, the effects of four thermal regimes, i.e., control (C), cold acclimation (CA), rapid cold hardening (RCH), and fluctuating-acclimation (FA), were examined for their effects on cold tolerance, supercooling point (SCP), lower lethal temperature (LLT), and chill-coma recovery time (CCRT) of the red flour beetle. In addition, changes in cryoprotectant (trehalose, sorbitol, and myo-inositol) levels were investigated under each thermal treatment. The results documented a substantial enhancement in the SCP, cold hardiness, and cryoprotectant levels of the adults of T. castaneum under CA regimes. The lowest SCP, highest trehalose and myo-inositol contents, and, subsequently, the greatest survival rate were observed in cold-acclimated beetles. In addition, coordination between cryoprotectant level, SCP, and cold tolerance of the pest was observed. The highest and lowest CCRT were observed at control and CA, respectively. In RCH regime with the highest impact, LLT reached the lowest level of -22°C. As most of the mortality of T. castaneum occurred at a temperature above the SCP, so this pest could be considered as a chill-susceptible insect.

The human brain somatostatin interactome: SST binds selectively to P-type family ATPases

Somatostatin (SST) is a cyclic peptide that is understood to inhibit the release of hormones and neurotransmitters from a variety of cells by binding to one of five canonical G protein-coupled SST receptors (SSTR1 to SSTR5). Recently, SST was also observed to interact with the amyloid beta (Aβ) peptide and affect its aggregation kinetics, raising the possibility that it may bind other brain proteins. Here we report on an SST interactome analysis that made use of human brain extracts as biological source material and incorporated advanced mass spectrometry workflows for the relative quantitation of SST binding proteins. The analysis revealed SST to predominantly bind several members of the P-type family of ATPases. Subsequent validation experiments confirmed an interaction between SST and the sodium-potassium pump (Na+/K+-ATPase) and identified a tryptophan residue within SST as critical for binding. Functional analyses in three different cell lines indicated that SST might negatively modulate the K+ uptake rate of the Na+/K+-ATPase.

Engineering a murine cell line for the stable propagation of hamster prions

Prions are infectious protein aggregates that cause several fatal neurodegenerative diseases. Prion research has been hindered by a lack of cellular paradigms for studying the replication of prions from different species. Although hamster prions have been widely used to study prion replication in animals and within in vitro amplification systems, they have proved challenging to propagate in cultured cells. Because the murine catecholaminergic cell line CAD5 is susceptible to a diverse range of mouse prion strains, we hypothesized that it might also be capable of propagating nonmouse prions. Here, using CRISPR/Cas9-mediated genome engineering, we demonstrate that CAD5 cells lacking endogenous mouse PrP expression (CAD5-PrP^-/- cells) can be chronically infected with hamster prions following stable expression of hamster PrP. When exposed to the 263K, HY, or 139H hamster prion strains, these cells stably propagated high levels of protease-resistant PrP. Hamster prion replication required absence of mouse PrP, and hamster PrP inhibited the propagation of mouse prions. Cellular homogenates from 263K-infected cells exhibited prion seeding activity in the RT-QuIC assay and were infectious to naïve cells expressing hamster PrP. Interestingly, murine N2a neuroblastoma cells ablated for endogenous PrP expression were susceptible to mouse prions, but not hamster prions upon expression of cognate PrP, suggesting that CAD5 cells either possess cellular factors that enhance or lack factors that restrict the diversity of prion strains that can be propagated. We conclude that transfected CAD5-PrP^-/- cells may be a useful tool for assessing the biology of prion strains and dissecting the mechanism of prion replication.

The prion protein is embedded in a molecular environment that modulates transforming growth factor β and integrin signaling

At times, it can be difficult to discern if a lack of overlap in reported interactions for a protein-of-interest reflects differences in methodology or biology. In such instances, systematic analyses of protein-protein networks across diverse paradigms can provide valuable insights. Here, we interrogated the interactome of the prion protein (PrP), best known for its central role in prion diseases, in four mouse cell lines. Analyses made use of identical affinity capture and sample processing workflows. Negative controls were generated from PrP knockout lines of the respective cell models, and the relative levels of peptides were quantified using isobaric labels. The study uncovered 26 proteins that reside in proximity to PrP. All of these proteins are predicted to have access to the outer face of the plasma membrane, and approximately half of them were not reported to interact with PrP before. Strikingly, although several proteins exhibited profound co-enrichment with PrP in a given model, except for the neural cell adhesion molecule 1, no protein was highly enriched in all PrP-specific interactomes. However, Gene Ontology analyses revealed a shared association of the majority of PrP candidate interactors with cellular events at the intersection of transforming growth factor β and integrin signaling.

A ZIP6-ZIP10 heteromer controls NCAM1 phosphorylation and integration into focal adhesion complexes during epithelial-to-mesenchymal transition

The prion protein (PrP) evolved from the subbranch of ZIP metal ion transporters comprising ZIPs 5, 6 and 10, raising the prospect that the study of these ZIPs may reveal insights relevant for understanding the function of PrP. Building on data which suggested PrP and ZIP6 are critical during epithelial-to-mesenchymal transition (EMT), we investigated ZIP6 in an EMT paradigm using ZIP6 knockout cells, mass spectrometry and bioinformatic methods. Reminiscent of PrP, ZIP6 levels are five-fold upregulated during EMT and the protein forms a complex with NCAM1. ZIP6 also interacts with ZIP10 and the two ZIP transporters exhibit interdependency during their expression. ZIP6 contributes to the integration of NCAM1 in focal adhesion complexes but, unlike cells lacking PrP, ZIP6 deficiency does not abolish polysialylation of NCAM1. Instead, ZIP6 mediates phosphorylation of NCAM1 on a cluster of cytosolic acceptor sites. Substrate consensus motif features and in vitro phosphorylation data point toward GSK3 as the kinase responsible, and interface mapping experiments identified histidine-rich cytoplasmic loops within the ZIP6/ZIP10 heteromer as a novel scaffold for GSK3 binding. Our data suggests that PrP and ZIP6 inherited the ability to interact with NCAM1 from their common ZIP ancestors but have since diverged to control distinct posttranslational modifications of NCAM1.

NCAM1 Polysialylation: The Prion Protein's Elusive Reason for Being?

Much confusion surrounds the physiological function of the cellular prion protein (PrP^C). It is, however, anticipated that knowledge of its function will shed light on its contribution to neurodegenerative diseases and suggest ways to interfere with the cellular toxicity central to them. Consequently, efforts to elucidate its function have been all but exhaustive. Building on earlier work that uncovered the evolutionary descent of the prion founder gene from an ancestral ZIP zinc transporter, we recently investigated a possible role of PrP^C in a morphogenetic program referred to as epithelial-to-mesenchymal transition (EMT). By capitalizing on PrP^C knockout cell clones in a mammalian cell model of EMT and using a comparative proteomics discovery strategy, neural cell adhesion molecule-1 emerged as a protein whose upregulation during EMT was perturbed in PrP^C knockout cells. Follow-up work led us to observe that PrP^C regulates the polysialylation of the neural cell adhesion molecule NCAM1 in cells undergoing morphogenetic reprogramming. In addition to governing cellular migration, polysialylation modulates several other cellular plasticity programs PrP^C has been phenotypically linked to. These include neurogenesis in the subventricular zone, controlled mossy fiber sprouting and trimming in the hippocampal formation, hematopoietic stem cell renewal, myelin repair and maintenance, integrity of the circadian rhythm, and glutamatergic signaling. This review revisits this body of literature and attempts to present it in light of this novel contextual framework. When approached in this manner, a coherent model of PrP^C acting as a regulator of polysialylation during specific cell and tissue morphogenesis events comes into focus.

Prion Protein Deficiency Causes Diverse Proteome Shifts in Cell Models That Escape Detection in Brain Tissue

A popular method for studying the function of a given protein is to generate and characterize a suitable model deficient for its expression. For the prion protein (PrP), best known for its role in several invariably fatal neurodegenerative diseases, a natural choice, therefore, would be to undertake such studies with brain samples. We recently documented the surprising observation that PrP deficiency caused a loss or enhancement of NCAM1 polysialylation, dependent on the cell model used. To identify possible causes for this disparity, we set out to systematically investigate the consequence of PrP deficiency on the global proteome in brain tissue and in four distinct cell models. Here we report that PrP deficiency causes robust but surprisingly divergent changes to the global proteomes of cell models but has no discernible impact on the global brain proteome. Amongst >1,500 proteins whose levels were compared in wild-type and PrP-deficient models, members of the MARCKS protein family exhibited pronounced, yet cell model-dependent changes to their steady-state levels. Follow-up experiments revealed that PrP collaborates with members of the MARCKS protein family in its control of NCAM1 polysialylation. We conclude that the physiological function of PrP may be masked in analyses of complex brain samples but its cell-type specific influence on a lipid raft-based NCAM1-related cell biology comes to the fore in investigations of specific cell types.

The Prion Protein Controls Polysialylation of Neural Cell Adhesion Molecule 1 during Cellular Morphogenesis

Despite its multi-faceted role in neurodegenerative diseases, the physiological function of the prion protein (PrP) has remained elusive. On the basis of its evolutionary relationship to ZIP metal ion transporters, we considered that PrP may contribute to the morphogenetic reprogramming of cells underlying epithelial-to-mesenchymal transitions (EMT). Consistent with this hypothesis, PrP transcription increased more than tenfold during EMT, and stable PrP-deficient cells failed to complete EMT in a mammalian cell model. A global comparative proteomics analysis identified the neural cell adhesion molecule 1 (NCAM1) as a candidate mediator of this impairment, which led to the observation that PrP-deficient cells fail to undergo NCAM1 polysialylation during EMT. Surprisingly, this defect was caused by a perturbed transcription of the polysialyltransferase ST8SIA2 gene. Proteomics data pointed toward β-catenin as a transcriptional regulator affected in PrP-deficient cells. Indeed, pharmacological blockade or siRNA-based knockdown of β-catenin mimicked PrP-deficiency in regards to NCAM1 polysialylation. Our data established the existence of a PrP-ST8SIA2-NCAM signaling loop, merged two mature fields of investigation and offer a simple model for explaining phenotypes linked to PrP.

The Human Tau Interactome: Binding to the Ribonucleoproteome, and Impaired Binding of the Proline-to-Leucine Mutant at Position 301 (P301L) to Chaperones and the Proteasome

The tau protein is central to the etiology of several neurodegenerative diseases, including Alzheimer's disease, a subset of frontotemporal dementias, progressive supranuclear palsy and dementia following traumatic brain injury, yet the proteins it interacts with have not been studied using a systematic discovery approach. Here we employed mild in vivo crosslinking, isobaric labeling, and tandem mass spectrometry to characterize molecular interactions of human tau in a neuroblastoma cell model. The study revealed a robust association of tau with the ribonucleoproteome, including major protein complexes involved in RNA processing and translation, and documented binding of tau to several heat shock proteins, the proteasome and microtubule-associated proteins. Follow-up experiments determined the relative contribution of cellular RNA to the tau interactome and mapped interactions to N- or C-terminal tau domains. We further document that expression of P301L mutant tau disrupts interactions of the C-terminal half of tau with heat shock proteins and the proteasome. The data are consistent with a model whereby a higher propensity of P301L mutant tau to aggregate may reflect a perturbation of its chaperone-assisted stabilization and proteasome-dependent degradation. Finally, using a global proteomics approach, we show that heterologous expression of a tau construct that lacks the C-terminal domain, including the microtubule binding domain, does not cause a discernible shift of the proteome except for a significant direct correlation of steady-state levels of tau and cystatin B.

CRISPR-Cas9-based knockout of the prion protein and its effect on the proteome

The molecular function of the cellular prion protein (PrPC) and the mechanism by which it may contribute to neurotoxicity in prion diseases and Alzheimer's disease are only partially understood. Mouse neuroblastoma Neuro2a cells and, more recently, C2C12 myocytes and myotubes have emerged as popular models for investigating the cellular biology of PrP. Mouse epithelial NMuMG cells might become attractive models for studying the possible involvement of PrP in a morphogenetic program underlying epithelial-to-mesenchymal transitions. Here we describe the generation of PrP knockout clones from these cell lines using CRISPR-Cas9 knockout technology. More specifically, knockout clones were generated with two separate guide RNAs targeting recognition sites on opposite strands within the first hundred nucleotides of the Prnp coding sequence. Several PrP knockout clones were isolated and genomic insertions and deletions near the CRISPR-target sites were characterized. Subsequently, deep quantitative global proteome analyses that recorded the relative abundance of>3000 proteins (data deposited to ProteomeXchange Consortium) were undertaken to begin to characterize the molecular consequences of PrP deficiency. The levels of ∼ 120 proteins were shown to reproducibly correlate with the presence or absence of PrP, with most of these proteins belonging to extracellular components, cell junctions or the cytoskeleton.

An emerging role of the cellular prion protein as a modulator of a morphogenetic program underlying epithelial-to-mesenchymal transition

Knowledge of phenotypic changes the cellular prion protein (PrP(C)) contributes to may provide novel avenues for understanding its function. Here we consider data from functional knockout/down studies and protein-protein interaction analyses from the perspective of PrP's relationship to its ancestral ZIP metal ion transporting proteins. When approached in this manner, a role of PrP(C) as a modulator of a complex morphogenetic program that underlies epithelial-to-mesenchymal transition (EMT) emerges. To execute EMT, cells have to master the challenge to shift from cell-cell to cell-substrate modes of adherence. During this process, cell-cell junctions stabilized by E-cadherins are replaced by focal adhesions that mediate cell-substrate contacts. A similar reprogramming occurs during distinct organogenesis events that have been shown to rely on ZIP transporters. A model is presented that sees ZIP transporters, and possibly also PrP(C), affect this balance of adherence modes at both the transcriptional and post-translational levels.

The ZIP5 ectodomain co-localizes with PrP and may acquire a PrP-like fold that assembles into a dimer

The cellular prion protein (PrP(C)) was recently observed to co-purify with members of the LIV-1 subfamily of ZIP zinc transporters (LZTs), precipitating the surprising discovery that the prion gene family descended from an ancestral LZT gene. Here, we compared the subcellular distribution and biophysical characteristics of LZTs and their PrP-like ectodomains. When expressed in neuroblastoma cells, the ZIP5 member of the LZT subfamily was observed to be largely directed to the same subcellular locations as PrP(C) and both proteins were seen to be endocytosed through vesicles decorated with the Rab5 marker protein. When recombinantly expressed, the PrP-like domain of ZIP5 could be obtained with yields and levels of purity sufficient for structural analyses but it tended to aggregate, thereby precluding attempts to study its structure. These obstacles were overcome by moving to a mammalian cell expression system. The subsequent biophysical characterization of a homogeneous preparation of the ZIP5 PrP-like ectodomain shows that this protein acquires a dimeric, largely globular fold with an α-helical content similar to that of mammalian PrP(C). The use of a mammalian cell expression system also allowed for the expression and purification of stable preparations of Takifugu rubripes PrP-1, thereby overcoming a key hindrance to high-resolution work on a fish PrP(C).

SPG11 Presenting with Tremor

BACKGROUND

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurological diseases, which typically present with progressive lower extremity weakness and spasticity causing progressive walking difficulties. Complicating neurological or extraneurological features may be present.

CASE REPORT

We describe a 19-year-old male who was referred because of an action tremor of the hands; he later developed walking difficulties. Callosal atrophy was present on his cerebral magnetic resonance imaging scan, prompting genetic testing for SPG11, which revealed homozygous mutations.

DISCUSSION

The clinical features, differential diagnosis and management of SPG11, the most common form of autosomal recessive complicated HSP with a thin corpus callosum are discussed.

LIV-1 ZIP ectodomain shedding in prion-infected mice resembles cellular response to transition metal starvation

We recently documented the co-purification of members of the LIV-1 subfamily of ZIP (Zrt-, Irt-like Protein) zinc transporters (LZTs) with the cellular prion protein (PrP(C)) and, subsequently, established that the prion gene family descended from an ancestral LZT gene. Here, we begin to address whether the study of LZTs can shed light on the biology of prion proteins in health and disease. Starting from an observation of an abnormal LZT immunoreactive band in prion-infected mice, subsequent cell biological analyses uncovered a surprisingly coordinated biology of ZIP10 (an LZT member) and prion proteins that involves alterations to N-glycosylation and endoproteolysis in response to manipulations to the extracellular divalent cation milieu. Starving cells of manganese or zinc, but not copper, causes shedding of the N1 fragment of PrP(C) and of the ectodomain of ZIP10. For ZIP10, this posttranslational biology is influenced by an interaction between its PrP-like ectodomain and a conserved metal coordination site within its C-terminal multi-spanning transmembrane domain. The transition metal starvation-induced cleavage of ZIP10 can be differentiated by an immature N-glycosylation signature from a constitutive cleavage targeting the same site. Data from this work provide a first glimpse into a hitherto neglected molecular biology that ties PrP to its LZT cousins and suggest that manganese or zinc starvation may contribute to the etiology of prion disease in mice.

The ZIP-prion connection

The evolutionary origins of vertebrate prion genes had remained elusive until recently when multiple lines of evidence converged to the proposition that members of the prion gene family represent an ancient branch of a larger family of ZIP metal ion transporters. (1) A follow-up investigation which explored the mechanism of evolution in more detail led to the surprising conclusion that the emergence of the prion founder gene likely involved the reverse transcription of a spliced transcript of a LIV-1 ZIP predecessor gene. (2) The objective of this perspective is to discuss the possible significance of this reunion of ZIP and prion gene subfamilies for understanding the biology of the prion protein in health and disease. While a recent review article broadly introduced this area of research, (3) the emphasis here is to comment on some of the more pertinent concepts, experimental paradigms, ongoing developments and challenges.

Quantitative structure-activity relationships and docking studies of calcitonin gene-related peptide antagonists

Defining the role of calcitonin gene-related peptide in migraine pathogenesis could lead to the application of calcitonin gene-related peptide antagonists as novel migraine therapeutics. In this work, quantitative structure-activity relationship modeling of biological activities of a large range of calcitonin gene-related peptide antagonists was performed using a panel of physicochemical descriptors. The computational studies evaluated different variable selection techniques and demonstrated shuffling stepwise multiple linear regression to be superior over genetic algorithm-multiple linear regression. The linear quantitative structure-activity relationship model revealed better statistical parameters of cross-validation in comparison with the non-linear support vector regression technique. Implementing only five peptide descriptors into this linear quantitative structure-activity relationship model resulted in an extremely robust and highly predictive model with calibration, leave-one-out and leave-20-out validation R(2) of 0.9194, 0.9103, and 0.9214, respectively. We performed docking of the most potent calcitonin gene-related peptide antagonists with the calcitonin gene-related peptide receptor and demonstrated that peptide antagonists act by blocking access to the peptide-binding cleft. We also demonstrated the direct contact of residues 28-37 of the calcitonin gene-related peptide antagonists with the receptor. These results are in agreement with the conclusions drawn from the quantitative structure-activity relationship model, indicating that both electrostatic and steric factors should be taken into account when designing novel calcitonin gene-related peptide antagonists.

Effect of PITX2 knockdown on transcriptome of primary human trabecular meshwork cell cultures

PURPOSE

To identify genes whose expressions in primary human trabecular meshwork (TM) cell cultures are affected by the transcription factor pituitary homeobox 2 (PITX2) and to identify genes that may have roles in glaucoma. Known glaucoma causing genes account for disease in a small fraction of patients, and we aimed at identification of other genes that may have subtle and accumulative effects not easily identifiable by a genetic approach.

METHODS

Expression profiles derived using microarrays were compared between TM control cells and cells treated with PITX2 siRNAs using three protocols so as to minimize false positive and negative results. The first protocol was based on the commonly used B statistic. The second and third protocols were based on fold change in expression. The second protocol used a threshold of at least 2 fold change in expression, whereas the third protocol used ranking in fold change without setting a threshold. The likelihood of a selected gene being a true positive was considered to correlate with the number of protocols by which it was selected. By considering all genes that were selected by at least one protocol, the likelihood of false negatives was expected to decrease. Effects on a subset of selected genes were verified by real time PCR, western blots, and immunocytochemistry. Effects on ALDH1A1, were further pursued because its protein product, aldehyde dehydrogenase 1 family, member A1, has roles in oxidative stress and because oxidative stress is known to be relevant to the etiology of glaucoma.

RESULTS

The expression level of 41 genes was assessed by to be possibly affected by PITX2 knockdown. Twenty one genes were down-regulated and twenty were upregulated. The expression of five genes was assessed to be altered by all three analysis protocols. The five genes were DIRAS3 (DIRAS family, GTP-binding RAS-like 3), CXCL6 (chemokine (C-X-C motif) ligand 6), SAMD5 (sterile alpha motif domain containing 5), CBFB (core-binding factor, beta subunit), and MEIS2 (meis homeobox 2). Real time PCR experiments verified results on a subset of genes tested. Notably, the results were also confirmed in two independent TMs. Effects on CXCL6 and ALDH1A1 were also confirmed by western blots, and effects on ALDH1A1 were further shown by immunocytochemistry. Data consistent with PITX2 involvement in ALDH1A1 mediated response to oxidative stress were presented.

CONCLUSIONS

Bioinformatics tools revealed that the genes identified affect functions and pathways relevant to glaucoma. Involvement of PITX2 in expression of some of the genes and in some of the pathways is being reported here for the first time. As many of the genes identified have not been studied vis-à-vis glaucoma, we feel they introduce new candidates for understanding this devastating disease.

Identification of ALOX5 as a gene regulating adiposity and pancreatic function

AIMS/HYPOTHESIS

We previously used an integrative genetics approach to demonstrate that 5-lipoxygenase (5-LO) deficiency in mice (Alox5 (-/-)) protects against atherosclerosis despite increasing lipid levels and fat mass. In the present study, we sought to further examine the role of 5-LO in adiposity and pancreatic function.

METHODS

Alox5 (-/-) and wild-type (WT) mice were characterised with respect to adiposity and glucose/insulin metabolism using in vivo and in vitro approaches. The role of ALOX5 in pancreatic function in human islets was assessed through short interfering RNA (siRNA) knockdown experiments.

RESULTS

Beginning at 12 weeks of age, Alox5 (-/-) mice had significantly increased fat mass, plasma leptin levels and fasting glucose levels, but lower fasting insulin levels (p<0.05). Although Alox5 (-/-) mice did not exhibit insulin resistance, they had impaired insulin secretion in response to a bolus glucose injection. Histological analyses revealed that Alox5 (-/-) mice had increased islet area, beta cell nuclear size, and numbers of beta cells/mm(2) islet (p<0.05), indicative of both hyperplasia and hypertrophy. Basal and stimulated insulin secretion in isolated Alox5 (-/-) islets were significantly lower than in WT islets (p<0.05) and accompanied by a three- to fivefold decrease in the expression of the genes encoding insulin and pancreatic duodenal homeobox 1 (Pdx1). Direct perturbation of ALOX5 in isolated human islets with siRNA decreased insulin and PDX1 gene expression by 50% and insulin secretion by threefold (p<0.05).

CONCLUSIONS/INTERPRETATION

These results provide strong evidence for pleiotropic metabolic effects of 5-LO on adiposity and pancreatic function and may have important implications for therapeutic strategies targeting this pathway for the treatment of cardiovascular disease.

Genetic locus in mice that blocks development of atherosclerosis despite extreme hyperlipidemia

The genes contributing to the common forms of atherosclerosis are largely unknown. One approach to dissecting complex traits such as atherosclerosis is to use animal models, such as the mouse, to map and characterize the genetic loci involved. We now report the identification of a locus for aortic lesion formation on mouse chromosome 6 that exhibits a highly significant lod score of 6.7 in a genetic cross between the susceptible strain, C57BL/6J, and the resistant strain, CAST/Ei. The locus was confirmed by constructing a congenic strain in which the chromosome 6 segment from CAST/Ei was transferred to a C57BL/6J background in a series of backcrosses. The congenic strain was almost completely resistant to diet-induced atherosclerosis. The chromosome 6 segment was also transferred onto the background of an LDL receptor-null mutation and resulted again in almost complete resistance to aortic lesion formation. This locus also influenced insulin levels but did not affect plasma lipoprotein levels, blood pressure, or body fat. The chromosome 6 gene, which we call Artles (for arterial lesions), did not affect endothelial cell responses to oxidized LDL, but lesion formation was partially reduced through bone marrow transplantation. The locus contains the candidate gene peroxisome proliferator-activated receptor-gamma, and the congenic mice exhibited significantly reduced expression of peroxisome proliferator-activated receptor-gamma.

Genetic control of HDL levels and composition in an interspecific mouse cross (CAST/Ei x C57BL/6J)

Strain CAST/Ei (CAST) mice exhibit unusually low levels of high density lipoproteins (HDL) as compared with most other strains of mice, including C57BL/6J (B6). This appears to be due in part to a functional deficiency of lecithin:cholesterol acyltransferase (LCAT). LCAT mRNA expression in CAST mice is normal, but the mice exhibit several characteristics consistent with functional deficiency. First, the activity and mass of LCAT in plasma and in HDL of CAST mice were reduced significantly. Second, the HDL of CAST mice were relatively poor in phospholipids and cholesteryl esters, but rich in free cholesterol and apolipoprotein A-I (apoA-I). Third, the adrenals of CAST mice were depleted of cholesteryl esters, a phenotype similar to that observed in LCAT- and acyl-CoA:cholesterol acyltransferase-deficient mice. Fourth, in common with LCAT-deficient mice, CAST mice contained triglyceride-rich lipoproteins with "panhandle"-like protrusions. To examine the genetic bases of these differences, we studied HDL lipid levels in an intercross between strain CAST and the common laboratory strain B6 on a low fat, chow diet as well as a high fat, atherogenic diet. HDL levels exhibited complex inheritance, as 12 quantitative trait loci with significant or suggestive likelihood of observed data scores were identified. Several of the loci occurred over plausible candidate genes and these were investigated. The results indicate that the functional LCAT deficiency is unlikely to be due to variations of the LCAT gene. Our results suggest that novel genes are likely to be important in the control of HDL metabolism, and they provide evidence of genetic factors influencing the interaction of LCAT with HDL.

Role of group II secretory phospholipase A2 in atherosclerosis: 1. Increased atherogenesis and altered lipoproteins in transgenic mice expressing group IIa phospholipase A2

Some observations have suggested that the extracellular group IIa phospholipase A2 (sPLA2), previously implicated in chronic inflammatory conditions such as arthritis, may contribute to atherosclerosis. We have examined this hypothesis by studying transgenic mice expressing the human enzyme. Compared with nontransgenic littermates, the transgenic mice exhibited dramatically increased atherosclerotic lesions when maintained on a high-fat, high-cholesterol diet. Surprisingly, the transgenic mice also exhibited significant atherosclerotic lesions when maintained on a low-fat chow diet. Immunohistochemical staining indicated that sPLA2 was present in the atherosclerotic lesions of the transgenic mice. On both chow and atherogenic diets, the transgenic mice exhibited decreased levels of HDLs and slightly increased levels of LDLs compared with nontransgenic littermates. These data indicate that group IIa sPLA2 may promote atherogenesis, in part, through its effects on lipoprotein levels. These data also provide a possible mechanism for the observation that there is an increased incidence of coronary artery disease in many chronic inflammatory diseases.

Genetic loci controlling body fat, lipoprotein metabolism, and insulin levels in a multifactorial mouse model

We analyzed the inheritance of body fat, leptin levels, plasma lipoprotein levels, insulin levels, and related traits in an intercross between inbred mouse strains CAST/Ei and C57BL/6J. CAST/Ei mice are unusually lean, with only approximately 8% of body weight as fat, whereas C57BL/6J mice have approximately 18% body fat. Quantitative trait locus analysis using > 200 F2 mice revealed highly significant loci (lod scores > 4.3) on chromosomes 2 (three separate loci) and 9 that contribute to mouse fat-pad mass for mice on a high-fat diet. Some loci also influenced plasma lipoprotein levels and insulin levels either on chow or high-fat diets. Two loci for body fat and lipoprotein levels (on central and distal chromosome 2) coincided with a locus having strong effects on hepatic lipase activity, an activity associated with visceral obesity and lipoprotein levels in humans. A locus contributing to plasma leptin levels (lod score 5.3) but not obesity was identified on chromosome 4, near the leptin receptor gene. These data identify candidate regions and candidate genes for studies of human obesity and diabetes, and suggest obesity is highly complex in terms of the number of genetic factors involved. Finally, they support the existence of specific genetic interactions between body fat, insulin metabolism, and lipoprotein metabolism.

Mapping a gene for combined hyperlipidaemia in a mutant mouse strain

Familial combined hyperlipidaemia (FCHL) is a common, multifactorial disorder associated with elevated levels of plasma triglyceride, cholesterol, or both. A characteristic feature is increased secretion of very low density lipoproteins (VLDL) and apolipoprotein B (apoB). Although FCHL is the most common cause of premature coronary artery disease (CAD), accounting for over 10% of cases, its aetiology remains largely unknown. One powerful approach to the dissection of complex genetic traits involves the use of animal models. We have identified a mouse strain, HcB-19/Dem (HcB-19), which exhibits hypertriglyceridaemia, hypercholesterolaemia and elevated levels of plasma apoB. Like FCHL patients, HcB-19 mice also exhibit increased secretion of triglyceride-rich lipoproteins, and their hyperlipidaemia becomes progressively more severe with age. It is likely that the hyperlipidaemia results from a mutation of a novel gene that arose during development of strain HcB-19. We mapped the hyperlipidaemia gene (Hyplip1) to the distal portion of mouse chromosome 3. This region is syntenic to human chromosome 1q21-q23, which has recently been shown to harbour a gene associated with FCHL in families from a Finnish isolate.

Amino terminus of apolipoprotein B suffices to produce recognition of malondialdehyde-modified low density lipoprotein by the scavenger receptor of human monocyte-macrophages

Malondialdehyde, a product of lipid peroxidation, produces threshold conversion of low density lipoprotein (LDL) to a form recognized by type I and type II scavenger receptors of monocyte-macrophages. To investigate whether localized domains of human apoB-100 protein provide recognition determinants, we tested the ability of several different apoB-bearing particles to interact with the scavenger receptor of human monocyte-macrophages. Genetically engineered, carboxyl-terminally truncated apoB proteins assembled into lipoprotein form were labeled by fluorescent dye. Fluorescence microscopy and quantitative fluorescent spectrophotometry showed that purified particles containing as little as 23% of the apoB amino-terminus were internalized by the scavenger receptor after, but not before, malondialdehyde modification. There was no recognition of the particles by the LDL receptor. Similar results were obtained with human plasma LDL homozygous for carboxyl-terminally truncated apoB-45.2. Liposome-incorporated fusion protein containing apoB residues 547-735 displayed specific uptake by the scavenger receptor without modification by malondialdehyde. In contrast, fusion proteins containing apoB residues 3,029-3,133 or a short amino terminal segment failed to interact. Thus, primary sequence presented by residues 1-1,084 sufficed to produce recognition of modified LDL by the scavenger receptor. These receptor-combining domains were sequestered when secreted in lipoprotein form and were expressed upon malondialdehyde modification. When packaged exogenously in liposome form, fusion protein containing apoB residues 547-735, containing approximately 4% of the primary sequence, mediated scavenger receptor-dependent uptake and hydrolysis. Our findings provide an additional function or the amino-terminal region of apoB and demonstrate that primary sequence presented by the first 2% of apoB-100 protein suffices to produce recognition on malondialdehyde-modified LDL by the scavenger receptor of human monocyte-macrophages.

Genetic regulation of cholesterol homeostasis: chromosomal organization of candidate genes

As part of an effort to dissect the genetic factors involved in cholesterol homeostasis in the mouse model, we report the mapping of 12 new candidate genes using linkage analysis. The genes include: cytoplasmic HMG-CoA synthase (Hmgcs 1, Chr 13), mitochondrial synthase (Hmgcs 2, Chr 3), a synthase-related sequence (Hmgcs 1-rs, Chr 12), mevalonate kinase (Mvk, Chr 5), farnesyl diphosphate synthase (Fdps, Chr 3), squalene synthase (Fdft 1, Chr 14), acyl-CoA:cholesterol acyltransferase (Acact, Chr 1), sterol regulatory element binding protein-1 (Srebf1, Chr 8) and -2 (Srebf2, Chr 15), apolipoprotein A-I regulatory protein (Tcfcoup2, Chr 7), low density receptor-related protein-related sequence (Lrp-rs, Chr 10), and Lrp-associated protein (Lrpap 1, Chr 5). In addition, the map positions for several lipoprotein receptor genes were refined. These genes include: low density lipoprotein receptor (Ldlr, Chr 9), very low density lipoprotein receptor (Vldlr, Chr 19), and glycoprotein 330 (Gp330, Chr 2). Some of these candidate genes are located within previously defined chromosomal regions (quantitative trait loci, QTLs) contributing to plasma lipoprotein levels, and Acact maps near a mouse mutation, ald, resulting in depletion of cholesteryl esters in the adrenals. The combined use of QTL and candidate gene mapping provides a powerful means of dissecting complex traits such as cholesterol homeostasis.

Genetic factors in lipoprotein metabolism. Analysis of a genetic cross between inbred mouse strains NZB/BINJ and SM/J using a complete linkage map approach

A genetic cross was constructed from two parental inbred strains of mice, NZB/BINJ and SM/J, which differ markedly in their plasma lipoprotein levels. Plasma lipid and apolipoprotein values were measured in 184 F2 progeny on a normal chow diet and on an atherogenic diet. Genetic markers were typed at 126 loci spanning all chromosomes except the Y. Statistical analysis revealed significant linkage or suggestive linkage of lipoprotein levels with markers on a number of chromosomes. Chromosome 1 markers were linked to levels of total cholesterol (lod 5.9) and high density lipoprotein (HDL) cholesterol (lod 8.1), chromosome 5 markers were linked to levels of total cholesterol (lod 6.7) and HDL cholesterol (lod 5.6), and chromosome 7 markers were linked to levels of total plasma triglycerides (lod 5.1) and free fatty acids (lod 5.6). Plasma apoAII levels were linked to the apoAII gene (lod score 19.6) and were highly correlated with plasma HDL cholesterol levels (r = 0.63, P = 0.0001), indicating that apoAII expression influences HDL cholesterol levels. Molecular studies suggested that structural differences in the apoAII polypeptide of the two strains may contribute to differences in clearance of the protein.

Localization of murine macrophage inducible nitric oxide synthase to mouse chromosome 11

There are at least three distinct nitric oxide (NO) synthase genes. Brain and endothelial NO synthases are constitutively synthesized, while NO synthase is inducible by cytokines in macrophages. We have utilized a backcross of (C57BL/6J x Mus spretus) x C57BL/6J to map the inducible NO synthase (Nos2). We report the chromosomal mapping of Nos2 to mouse chromosome 11, 3.3 cM proximal to Scya2.

Linkage mapping of 40 randomly isolated liver cDNA clones in the mouse

We report the chromosomal mapping of 43 loci for 40 randomly isolated mouse liver cDNA clones by linkage analysis in an interspecific backcross of ((C57BL/6J x Mus spretus) x C57BL/6J). The clones were sequenced from both sides and a subset was examined for expression in various mouse tissues. Fifteen of the 40 mapped cDNA clones are either identical or strongly related to known sequences in GenBank, while 25 represent new genes. Additional loci mapped in this cross include 53 simple sequence repeat polymorphisms and 40 restriction fragment length variants from previously characterized cDNA markers. Nine homologous human genes were identified for 7 mouse liver cDNA clones. One clone that maps to mouse chromosome 3 (D3Ucla1) identified a novel homologous segment (synteny) on human chromosome 18q23 (D18S372E). These studies provide linkage mapping and initial characterization of random cDNA clones that may provide a resource for the positional candidate cloning of disease genes.

Chromosomal organization of mammalian POU domain factors

We present the chromosomal locations in mouse of eight new members of the mammalian POU domain family of transcriptional regulators. Chromosomal assignments were made for Brn-1 (Chr 1), Brn-2 (Chr 4), Brn-4 (Chr X), Brn-3.0 (Chr 14), Brn-3.1 (Chr 18), Brn-5.0 (Chr 15), Skn-1a/i (Chr 9), and Sprm-1 (Chr 13) in addition to the previously reported Pit-1 (Chr 16), Tst-1 (Chr 4), Oct-3/4 (Chr 17), Oct-1 (Chr 1), and Oct-2 (Chr 7) genes. Several conclusions have emerged from this analysis. First, among the most highly related family members (Brn-1, Brn-2, Brn-4, and Tst-1; Brn-3.0 and Brn-3.1; Oct-1, Oct-2, and Skn-1a/i) no chromosomal linkage is noted. Second, no clusters of genes are observed, irrespective of homology. Finally, no obvious linkages to genes for known additional regulatory factors with a specific origin of cell type are apparent. Thus, members of this large gene family, presumably arising as duplication events from common ancestral genes, apparently function in distinct chromosomal milieu under independent regulation. Some of these newly localized genes map in close proximity to existing mouse mutations.

Two members of the S-lac lectin gene family, LGALS1 and LGALS2, reside in close proximity on human chromosome 22q12-q13

S-lac lectins are a family of soluble lactose-binding proteins thought to function in the control of cell growth. We now report the chromosomal mapping of two members of the family, termed L-14-I and L-14-II, to the q12-q13 region of human chromosome 22, suggesting the possibility of a cluster of genes for lactose-binding proteins.

Influence of the apoA-II gene locus on HDL levels and fatty streak development in mice

Previous studies have shown that distal mouse chromosome 1 contains the apolipoprotein AII (apoAII) gene, encoding the second most abundant apolipoprotein in high density lipoproteins (HDLs), as well as a gene termed Ath-1 that controls aortic fatty streak development and HDL cholesterol levels in response to a high-fat, high-cholesterol diet. We report genetic studies confirming that the genes are distinct. Using molecular markers for mouse chromosome 1, we have further mapped the two genes, and our results indicate that they are separated by a minimum of 2 cM. We also report evidence that in mice on a low-fat chow diet, the apoAII gene locus influences HDL cholesterol levels. Thus, statistical analysis of two sets of recombinant inbred strains revealed concordant segregation patterns of HDL cholesterol levels and the apoAII gene locus. The effect of apoAII expression on HDL cholesterol levels was further tested by using a congenic strain that exhibits increased apoAII synthesis in comparison to the background strain. The results support the concept that increased synthesis of apoAII results in increased HDL cholesterol levels. Unexpectedly, increased expression of apoAII appeared to promote rather than retard aortic fatty streak development.

Cloning of the human cholesterol 7 alpha-hydroxylase gene (CYP7) and localization to chromosome 8q11-q12

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is a microsomal cytochrome P450 that catalyzes the first step in bile acid synthesis. In this paper, we describe the cloning, characterization, and chromosomal mapping of the human 7 alpha-hydroxylase gene (CYP7). The gene spans 10 kb and contains six exons and five introns. The exon-intron boundaries are completely conserved between the human and rat genes. Sequencing of the 5' flanking region revealed consensus recognition sequences for a number of liver-specific transcription factors. The human CYP7 gene was mapped to chromosome 8q11-q12 using both mouse-human somatic cell hybrids and in situ chromosomal hybridization studies. A total of four single-stranded conformation-dependent DNA polymorphisms and an Alu sequence-related polymorphism were identified. Of the individuals analyzed, 80% were heterozygous for at least one of these five polymorphisms. The localization and characterization of the human 7 alpha-hydroxylase gene, as well as the identification of polymorphisms, provide the molecular tools necessary to investigate the role of this gene in disorders of cholesterol and bile acid metabolism.

The L-isoaspartyl/D-aspartyl protein methyltransferase gene (PCMT1) maps to human chromosome 6q22.3-6q24 and the syntenic region of mouse chromosome 10

We have mapped the genes for the human and mouse L-isoaspartyl/D-aspartyl protein carboxyl methyltransferase (EC 2.1.1.77) using cDNA probes. We determined that the human gene is present in chromosome 6 by Southern blot analysis of DNA from a panel of mouse-human somatic cell hybrids. In situ hybridization studies allowed us to confirm this identification and further localize the human gene (PCMT1) to the 6q22.3-6q24 region. By analyzing the presence of an EcoRI polymorphism in DNA from backcrosses of C57BL/6J and Mus spretus strains of mice, we localized the mouse gene (Pcmt-1) to chromosome 10, at a position 8.2 +/- 3.5 cM proximal to the Myb locus. This region of the mouse chromosome is homologous to the human 6q24 region.

Mechanisms controlling competence gene expression in murine fibroblasts stimulated with minimally modified LDL

Mildly oxidized low density lipoprotein (minimally modified low density lipoprotein [MM-LDL] is capable of inducing gene expression in cells of the artery wall. In this study, we investigated the mechanisms that control the mRNA expression of JE, KC, c-myc, and c-fos in quiescent mouse L-cell fibroblasts stimulated with MM-LDL. The data demonstrate that MM-LDL induces increases greater than or equal to 20-fold in the levels of transcripts of these genes within 15-60 minutes. Of the four genes examined, JE and KC mRNA showed the greatest response to MM-LDL. The pattern of induction by MM-LDL is distinct from that observed in fibroblasts stimulated with serum, a known inducer of these genes. Treatment with cycloheximide (10 micrograms/ml) did not block the MM-LDL-induced increase in the mRNA levels of these genes. The increase of JE and KC mRNA levels in response to MM-LDL could be blocked by treatment with actinomycin D (5 micrograms/ml). In nuclear runoff studies, MM-LDL increased the transcription rate of JE and KC at 4 hours by 13-fold and fivefold, respectively. Small but reproducible stimulations of c-fos and c-myc transcription by MM-LDL were also observed. In addition, the half-life of JE mRNA was increased after addition of MM-LDL to fibroblasts, suggesting that the MM-LDL-induced accumulation of these mRNAs might be accomplished by both transcriptional and posttranscriptional mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential accumulation of intimal monocyte-macrophages relative to lipoproteins and lipofuscin corresponds to hemodynamic forces on cardiac valves in mice

We have studied the distribution of monocyte-macrophages, lipids, and lipoproteins in sections of aorta and aortic valves from mice fed an atherogenic diet. By immunocytochemical analysis with Mac-1 and F4/80 antibodies, apolipoprotein B antibody, and oil red O staining, three discrete regions were identified: 1) the aortic wall of the sinus of Valsalva, which contained deposits of lipid that colocalized with lipoproteins and monocyte-macrophages; 2) the sides of the aortic valve leaflets facing the ventricle, which did not contain lipids or lipoproteins but which were lined with macrophages that colocalized with lipofuscin; and 3) the sides of the leaflets facing the aorta, which did not contain lipids, lipoproteins, monocyte-macrophages, or lipofuscin deposits. This pattern of distribution resembles the expected distribution of mechanical forces, especially those of systolic blood flow, which in the three areas are predominantly 1) low-shear disturbed flow, 2) high-shear laminar flow, and 3) low-shear laminar flow, respectively. These findings suggest that lesions in the mouse closely resemble early atherosclerotic lesions in humans and other primates with respect to monocyte-macrophage and lipoprotein accumulation. The results also strikingly demonstrate that the accumulation of monocyte-macrophages and lipoproteins can occur independently, with spatial differences corresponding to the distribution of hemodynamic forces.

Minimally modified low density lipoprotein is biologically active in vivo in mice

Minimally modified low density lipoprotein (MM-LDL), derived by mild iron oxidation or prolonged storage at 4 degrees C, has been shown to induce certain inflammatory responses in vascular cells in tissue culture. These include induction of monocyte (but not neutrophil) adherence to endothelial cells (EC), induction of EC production of colony stimulating factors (CSF), and induction of EC and smooth muscle cell production of monocyte chemotactic protein (MCP-1). To test for biologic activity in vivo, microgram quantities of MM-LDL were injected into mice, sera were assayed for CSF activity, and tissues were subjected to Northern analysis. After injection of MM-LDL, CSF activity increased approximately 7-26-fold but remained near control levels after injection of native LDL. Essentially all of the induced CSF activity was due to macrophage CSF as judged by antibody inhibition. Injection of MM-LDL into a mouse strain (C3H/HeJ) that is resistant to bacterial LPS gave similar results, indicating that the induction of CSF was not due to contaminating LPS and suggesting that there are differences in the pathways by which LPS and MM-LDL trigger cytokine production. In addition, after injection of MM-LDL, mRNA for JE, the mouse homologue of MCP-1, was markedly induced in various tissues, but was not induced after injection of native LDL. We conclude, therefore, that MM-LDL is biologically active in vivo and may contribute to the early stages of atherosclerosis by acting as an inflammatory agent.

Localization of monocyte chemotactic protein-1 gene (SCYA2) to human chromosome 17q11.2-q21.1

Monocyte chemotactic protein-1 (MCP-1) is a member of the small inducible gene (SIG) family. It has been shown to play a role in the recruitment of monocytes to sites of injury and infection. By analysis of a panel of somatic cell hybrids, we have localized the MCP-1 gene, designated SCYA2, to human chromosome 17. In situ hybridization confirmed this assignment and further localized the gene to 17q11.2-q21.1.

Dietary regulation of fibrinolytic factors

W examined the short-term effects of a high-complex carbohydrate, low fat diet on the plasmin-dependent fibrinolytic pathway. A population of 27 adult American Caucasians exposed to the diet for 3 weeks showed highly significant reductions in the levels of plasminogen (P = 0.0001), tissue plasminogen activator (tPA) (P = 0.0001) and plasminogen activator inhibitor (tPAI) (P = 0.0017). Fibrinogen levels also decreased, but the changes did not reach statistical significance (P = 0.07). In contrast, the levels of the Lpa(a) lipoprotein, a potential inhibitor of fibrinolysis, remained remarkably constant despite a marked decrease in the levels of apolipoprotein B, a major constituent of Lp(a). Correlations between the levels of tPA, tPAI and plasma triglyceride were observed among the individuals both before and after the dietary challenge. Although the mechanisms responsible for the effects are unknown, the dramatic responsiveness of the thrombolytic pathway to dietary challenge is likely to be of importance in understanding the etiology of coronary artery disease and other vascular disorders.