The apolipoprotein(a) gene is regulated by sex hormones and acute-phase inducers in YAC transgenic mice

Genetics and Pathophysiological Mechanisms of Lipoprotein(a)-Associated Cardiovascular Risk

Elevated lipoprotein(a) is a genetically transmitted codominant trait that is an independent risk driver for cardiovascular disease. Lipoprotein(a) concentration is heavily influenced by genetic factors, including LPA kringle IV-2 domain size, single-nucleotide polymorphisms, and interleukin-1 genotypes. Apolipoprotein(a) is encoded by the LPA gene and contains 10 subtypes with a variable number of copies of kringle -2, resulting in >40 different apolipoprotein(a) isoform sizes. Genetic loci beyond LPA, such as APOE and APOH, have been shown to impact lipoprotein(a) levels. Lipoprotein(a) concentrations are generally 5% to 10% higher in women than men, and there is up to a 3-fold difference in median lipoprotein(a) concentrations between racial and ethnic populations. Nongenetic factors, including menopause, diet, and renal function, may also impact lipoprotein(a) concentration. Lipoprotein(a) levels are also influenced by inflammation since the LPA promoter contains an interleukin-6 response element; interleukin-6 released during the inflammatory response results in transient increases in plasma lipoprotein(a) levels. Screening can identify elevated lipoprotein(a) levels and facilitate intensive risk factor management. Several investigational, RNA-targeted agents have shown promising lipoprotein(a)-lowering effects in clinical studies, and large-scale lipoprotein(a) testing will be fundamental to identifying eligible patients should these agents become available. Lipoprotein(a) testing requires routine, nonfasting blood draws, making it convenient for patients. Herein, we discuss the genetic determinants of lipoprotein(a) levels, explore the pathophysiological mechanisms underlying the association between lipoprotein(a) and cardiovascular disease, and provide practical guidance for lipoprotein(a) testing.

Lipoprotein(a): Just an Innocent Bystander in Arterial Hypertension?

Elevated plasma lipoprotein(a) [Lp(a)] is a relatively common and highly heritable trait conferring individuals time-dependent risk of developing atherosclerotic cardiovascular disease (CVD). Following its first description, Lp(a) triggered enormous scientific interest in the late 1980s, subsequently dampened in the mid-1990s by controversial findings of some prospective studies. It was only in the last decade that a large body of evidence has provided strong arguments for a causal and independent association between elevated Lp(a) levels and CVD, causing renewed interest in this lipoprotein as an emerging risk factor with a likely contribution to cardiovascular residual risk. Accordingly, the 2022 consensus statement of the European Atherosclerosis Society has suggested inclusion of Lp(a) measurement in global risk estimation. The development of highly effective Lp(a)-lowering drugs (e.g., antisense oligonucleotides and small interfering RNA, both blocking LPA gene expression) which are still under assessment in phase 3 trials, will provide a unique opportunity to reduce "residual cardiovascular risk" in high-risk populations, including patients with arterial hypertension. The current evidence in support of a specific role of Lp(a) in hypertension is somehow controversial and this narrative review aims to overview the general mechanisms relating Lp(a) to blood pressure regulation and hypertension-related cardiovascular and renal damage.

Lipoprotein(a) and coronary artery disease in Chinese postmenopausal female patients: a large cross-sectional cohort study

Background

It has been reported that lipoprotein(a) (Lp(a)) is associated with the risk of cardiovascular disease. The present study aimed to examine the association of Lp(a) levels with the presence and severity of coronary artery disease (CAD) in female patients.

Methods

A total of 3712 female patients who received coronary angiography were consecutively enrolled. The levels of Lp(a) were measured and compared among patients with or without CAD, myocardial infarction and menopause. Spearman correlation analysis and logistic regression analysis were used to examine the association of Lp(a) with the presence of CAD and the severity of coronary atherosclerosis assessed by Gensini score (GS).

Results

The average of Lp(a) levels was elevated as age increased in female subjects. Notably, women after menopause had higher Lp(a) levels compared with that before menopause (16.8 mg/dL (IQR 7.54–41.12 mg/dL) vs 14.7 mg/dL (IQR 6.72–30.82 mg/dL), p=0.002). Furthermore, multiple logistic regression analysis identified that Lp(a)>30 mg/dL was an independent risk factor of CAD in the postmenopausal females (OR: 1.33, 95% CI: 1.08 to 1.63, p=0.007). Finally, Lp(a) had a positive correlation with GS (r=0.11, p<0.001), and Lp(a)>30 mg/dL was an independent risk factor for high GS (OR: 1.43, 95% CI: 1.14 to 1.79, p=0.02) in the postmenopausal females.

Conclusion

Circulating Lp(a) levels were independently associated with the presence and severity of CAD in the postmenopausal females, suggesting that Lp(a) may be useful for prevention and risk-stratification of CAD in female individuals.

Lipoprotein(a) in postmenopausal women: assessment of cardiovascular risk and therapeutic options

INTRODUCTION

Lipoprotein(a) [Lp(a)], a low-density lipoprotein (LDL)-like particle, has been independently associated with increased cardiovascular disease (CVD) risk in various populations, such as postmenopausal women. The purpose of this narrative review is to present current data on the role of Lp(a) in augmenting CVD risk in postmenopausal women and focus on the available therapeutic strategies.

METHODS

PubMed was searched for English language publications until November 2015 under the following terms: "therapy" OR "treatment" AND ["lipoprotein (a)" OR "Lp(a)"] AND ("postmenopausal women" OR "menopausal women" OR "menopause").

RESULTS

Only hormone replacement therapy (mainly oral estrogens) and tibolone have been specifically studied in postmenopausal women and can reduce Lp(a) concentrations by up to 44%, although evidence indicating a concomitant reduction in CVD risk associated with Lp(a) is lacking. As alternative treatments for women who cannot, or will not, take hormonal therapies, niacin and the upcoming proprotein convertase subtilisin / kexin type 9 (PCSK-9) inhibitors are effective in reducing Lp(a) concentrations by up to 30%. Statins have minimal or no effect on Lp(a). However, data for these and other promising Lp(a)-lowering therapies including mipomersen, lomitapide, cholesterol-ester-transfer protein inhibitors and eprotirome are derived from studies in the general, mainly high CVD risk, population, and include only subpopulations of postmenopausal women.

CONCLUSIONS

Past, present and emerging therapies can reduce Lp(a) concentrations to a varying extent. Overall, it remains to be proven whether the aforementioned reductions in Lp(a) by these therapeutic options are translated into CVD risk reduction in postmenopausal women.

Disposition and Pharmacokinetics of a GalNAc3-Conjugated Antisense Oligonucleotide Targeting Human Lipoprotein (a) in Monkeys

Triantennary N-acetyl galactosamine (GalNAc₃)-conjugated antisense oligonucleotides (ASOs) have greatly improved potency due to receptor-mediated uptake into hepatocyte. The disposition and pharmacokinetics of ISIS 681257, a GalNAc₃-conjugated ASO, were studied in monkeys. Following subcutaneous (SC) injection, ISIS 681257 was rapidly absorbed into the systemic circulation, with peak plasma levels observed within hours after dosing. After reaching C_max, plasma concentrations rapidly declined in a multiexponential manner and were characterized by a dominant initial rapid distribution phase in which drug transferred to tissues from circulation, followed by a much slower terminal elimination phase (half-life of 4 weeks). Intact ISIS 681257 is the major full-length oligonucleotide species in plasma (≥70%). In tissues, the conjugated-GalNAc sugar moiety was rapidly metabolized, leaving the fully unconjugated form as the only full-length oligonucleotide detected at 48 h after dosing. Unconjugated ISIS 681257 cleared slowly from tissues with a half-life of 4 weeks. ISIS 681257 was highly bound to plasma proteins (>97% bound), which limited its urinary excretion. Disposition of ISIS 681257 in plasma and liver appeared nonlinear over the 1-40 mg/kg dose range studied. The plasma and liver tissue concentration data were well described by a population based mixed-effects modeling approach with Michaelis-Menten uptake from plasma to liver. Safety data from the study and the good exposure, as well as the extended half-life of the unconjugated ASO in the liver, support further development and less frequent dosing in Phase I clinical study.

Disposition and Pharmacology of a GalNAc3-conjugated ASO Targeting Human Lipoprotein (a) in Mice

Triantennary N-acetyl galactosamine (GalNAc₃)-conjugated antisense oligonucleotides (ASOs) have greatly improved potency via receptor-mediated uptake. In the present study, the in vivo pharmacology of a 2′-O-(2-methoxyethyl)-modified ASO conjugated with GalNAc₃ (ISIS 681257) together with its unmodified congener (ISIS 494372) targeting human apolipoprotein (a) (apo(a)), were studied in human LPA transgenic mice. Further, the disposition kinetics of ISIS 681257 was studied in CD-1 mice. ISIS 681257 demonstrated over 20-fold improvement in potency over ISIS 494372 as measured by liver apo(a) mRNA and plasma apo(a) protein levels. Following subcutaneous (SC) dosing, ISIS 681257 cleared rapidly from plasma and distributed to tissues. Intact ISIS 681257 was the major full-length oligonucleotide species in plasma. In tissues, however, GalNAc sugar moiety was rapidly metabolized and unconjugated ISIS 681257 accounted > 97% of the total exposure, which was then cleared slowly from tissues with a half-life of 7–8 days, similar to the half-life in plasma. ISIS 681257 is highly bound to plasma proteins (> 94% bound), which limited its urinary excretion. This study confirmed dose-dependent exposure to the parent drug ISIS 681257 in plasma and rapid conversion to unconjugated ASO in tissues. Safety data and the extended half-life support its further development and weekly dosing in phase 1 clinical studies.

Antisense inhibition of apolipoprotein (a) to lower plasma lipoprotein (a) levels in humans

Epidemiological, genetic association, and Mendelian randomization studies have provided strong evidence that lipoprotein (a) [Lp(a)] is an independent causal risk factor for CVD, including myocardial infarction, stroke, peripheral arterial disease, and calcific aortic valve stenosis. Lp(a) levels >50 mg/dl are highly prevalent (20% of the general population) and are overrepresented in patients with CVD and aortic stenosis. These data support the notion that Lp(a) should be a target of therapy for CVD event reduction and to reduce progression of aortic stenosis. However, effective therapies to specifically reduce plasma Lp(a) levels are lacking. Recent animal and human studies have shown that Lp(a) can be specifically targeted with second generation antisense oligonucleotides (ASOs) that inhibit apo(a) mRNA translation. In apo(a) transgenic mice, an apo(a) ASO reduced plasma apo(a)/Lp(a) levels and their associated oxidized phospholipid (OxPL) levels by 86 and 93%, respectively. In cynomolgus monkeys, a second generation apo(a) ASO, ISIS-APO(a)Rx, significantly reduced hepatic apo(a) mRNA expression and plasma Lp(a) levels by >80%. Finally, in a phase I study in normal volunteers, ISIS-APO(a)Rx ASO reduced Lp(a) levels and their associated OxPL levels up to 89 and 93%, respectively, with minimal effects on other lipoproteins. ISIS-APO(a)Rx represents the first specific and potent drug in clinical development to lower Lp(a) levels and may be beneficial in reducing CVD events and progression of calcific aortic valve stenosis.

Inhibition of neointima formation through DNA vaccination for apolipoprotein(a): a new therapeutic strategy for lipoprotein(a)

Lipoprotein(a) [Lp(a)] is an unique lipoprotein consisting of the glycoprotein apolipoprotein(a) [apo(a)] in low-density lipoprotein. Although Lp(a) is a well-known independent risk factor for cardiovascular disease; however, there is no drugs to decrease plasma Lp(a) level. Thus, to inhibit the biological activity of Lp(a), we developed DNA vaccine for apo(a) by the targeting to the selected 12 hydrophilic amino acids in the kringle-4 type 2 domain of apo(a). Hepatitis B virus core protein was used as an epitope carrier to enhance the immunogenicity. Intramuscular immunization with apo(a) vaccine resulted in the significant inhibition of neointima formation in carotid artery ligation model using Lp(a) transgenic mice, associated with anti-apo(a) antibody and decrease in vascular Lp(a) deposition. Overall, this study provided the first evidence that the pro-atherosclerotic actions of Lp(a) could be prevented by DNA vaccine directed against apo(a), suggesting a novel therapeutic strategy to treat cardiovascular diseases related to high Lp(a).

Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice

Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.

Generation of a novel rodent model for DYT1 dystonia

A mutation in the coding region of the Tor1A gene, resulting in a deletion of a glutamic acid residue in the torsinA protein (∆ETorA), is the major cause of the inherited autosomal-dominant early onset torsion dystonia (DYT1). The pathophysiological consequences of this amino acid loss are still not understood. Currently available animal models for DYT1 dystonia provided important insights into the disease; however, they differ with respect to key features of torsinA associated pathology. We developed transgenic rat models harboring the full length human mutant and wildtype Tor1A gene. A complex phenotyping approach including classical behavioral tests, electrophysiology and neuropathology revealed a progressive neurological phenotype in ∆ETorA expressing rats. Furthermore, we were able to replicate key pathological features of torsinA associated pathology in a second species, such as nuclear envelope pathology, behavioral abnormalities and plasticity changes. We therefore suggest that this rat model represents an appropriate new model suitable to further investigate the pathophysiology of ∆ETorA and to test for therapeutic approaches.

Lipoprotein(a) in Children of Asian Indian Descendants and Their Caucasian Neighbors: The Slovak Lipid Community Study

To elucidate a higher rate of premature cardiovascular disease (CVD) in Asian Indian descendants (Roma) in Slovakia, we investigated frequency distribution, correlates and relationship of lipoprotein(a) [Lp(a)] to family CVD risk factors in Roma children and their Caucasian neighbors. The study sample consisted of 607 healthy children aged 7-18 years (55% Roma, 48% male) as part of the biracial (Roma-Caucasian) Slovak Lipid Community Study. Overall, frequency distribution data of Lp(a) were highly skewed to low concentrations, with markedly higher Lp(a) levels in Roma than in Caucasian children (median and range, mg/dL: 14.5; 0-159.2 vs 6.2; 0-112.3, P < 0.001), regardless of age and gender. Lp(a) was positively correlated with apo B (0.159, P = 0.004) in Roma, and LDL cholesterol (0.170, P = 0.005) in Caucasian children. In addition, daily income of the family was negatively related with Lp(a) in Roma (-0.134, P = 0.036) while positively in Caucasians (0.136, P = 0.047). For both race groups, no significant association was found between Lp(a) and age, body mass index, mean arterial pressure, smoking, and physical activity. Also, no significant relationships were examined between serum Lp(a) levels >30 mg/dL in children and family CVD risk factors, except for diabetes mellitus in parents of Caucasian origin (OR 4.46; 95%CI: 1.23-16.20). In a multivariate analysis, daily income, LDL cholesterol or apo B explained ~7% of the variance of Lp(a). This study suggests a significantly higher serum Lp(a) levels in Roma than in Caucasian children and a small effect, in general, of relevant CVD risk factors on the variation of Lp(a) levels in childhood.

FGF19 signaling cascade suppresses APOA gene expression

OBJECTIVE

Lipoprotein(a) is a highly atherogenic lipoprotein, whose metabolism is poorly understood. Currently no safe drugs exists that lower elevated plasma lipoprotein(a) concentrations. We therefore focused on molecular mechanisms that influence apolipoprotein(a) (APOA) biosynthesis.

METHODS AND RESULTS

Transgenic human APOA mice (tg-APO mice) were injected with 1 mg/kg of recombinant human fibroblast growth factor 19 (FGF19). This led to a significant reduction of plasma APOA and hepatic expression of APOA. Incubation of primary hepatocytes of tg-APOA mice with FGF19 induced ERK1/2 phosphorylation and, in turn, downregulated APOA expression. Repression of APOA by FGF19 was abrogated by specific ERK1/2 phosphorylation inhibitors. The FGF19 effect on APOA was attenuated by transfection of primary hepatocytes with siRNA against the FGF19 receptor 4 (FGFR4). Using promoter reporter assays, mutation analysis, gel shift, and chromatin immune-precipitation assays, an Ets-1 binding element was identified at -1630/-1615bp region in the human APOA promoter. This element functions as an Elk-1 binding site that mediates repression of APOA transcription by FGF19.

CONCLUSIONS

These findings provide mechanistic insights into the transcriptional regulation of human APOA by FGF19. Further studies in the human system are required to substantiate our findings and to design therapeutics for hyper lipoprotein(a).

Farnesoid X receptor represses hepatic human APOA gene expression

High plasma concentrations of lipoprotein(a) [Lp(a), which is encoded by the APOA gene] increase an individual's risk of developing diseases, such as coronary artery diseases, restenosis, and stroke. Unfortunately, increased Lp(a) levels are minimally influenced by dietary changes or drug treatment. Further, the development of Lp(a)-specific medications has been hampered by limited knowledge of Lp(a) metabolism. In this study, we identified patients suffering from biliary obstructions with very low plasma Lp(a) concentrations that rise substantially after surgical intervention. Consistent with this, common bile duct ligation in mice transgenic for human APOA (tg-APOA mice) lowered plasma concentrations and hepatic expression of APOA. To test whether farnesoid X receptor (FXR), which is activated by bile acids, was responsible for the low plasma Lp(a) levels in cholestatic patients and mice, we treated tg-APOA and tg-APOA/Fxr-/- mice with cholic acid. FXR activation markedly reduced plasma concentrations and hepatic expression of human APOA in tg-APOA mice but not in tg-APOA/Fxr-/- mice. Incubation of primary hepatocytes from tg-APOA mice with bile acids dose dependently downregulated APOA expression. Further analysis determined that the direct repeat 1 element between nucleotides -826 and -814 of the APOA promoter functioned as a negative FXR response element. This motif is also bound by hepatocyte nuclear factor 4α (HNF4α), which promotes APOA transcription, and FXR was shown to compete with HNF4α for binding to this motif. These findings may have important implications in the development of Lp(a)-lowering medications.

Antisense oligonucleotide lowers plasma levels of apolipoprotein (a) and lipoprotein (a) in transgenic mice

OBJECTIVES

This study sought to assess whether an antisense oligonucleotide (ASO) directed to apolipoprotein (a) [apo(a)] reduces apo(a) and lipoprotein (a) [Lp(a)] levels in transgenic mouse models.

BACKGROUND

Elevated Lp(a) is a causal, independent, genetic risk factor for cardiovascular disease and myocardial infarction. Effective therapies to specifically lower plasma Lp(a) levels are lacking.

METHODS

Three transgenic mouse models were utilized: 8K-apo(a) mice expressing 8 kringle IV (KIV) repeats with a single copy of KIV-2; 8K-Lp(a) mice expressing both the 8K apo(a) plus human apolipoprotein B-100; and 12K-apo(a) mice expressing a 12K apo(a) with 3 KIV-2 repeats. The mice were treated intraperitoneally with saline, a control ASO, or ASO 144367 directed to KIV-2 for 4 to 6 weeks. Apo(a), Lp(a), and oxidized phospholipids present on human apoB (OxPL/h-apoB) or apo(a) [OxPL/apo(a)] were measured at baseline and on and off therapy.

RESULTS

ASO 144367 significantly reduced Lp(a) by 24.8% in 8K-Lp(a) mice, and reduced apo(a) levels by 19.2% in 8K-Lp(a) mice, 30.0% in 8K-apo(a) mice, and 86% in 12K-apo(a) mice; ASO 144367 also significantly reduced OxPL/apoB 22.4% in 8K-Lp(a) mice, and OxPL/apo(a) levels by 19.9% in 8K-Lp(a) mice, 22.1% in 8K-apo(a) mice, and 92.5% in 12K-apo(a) mice (p < 0.004, or less, for all). No significant changes occurred in Lp(a), apo(a), OxPL/apoB, or OxPL/apo(a) levels with control ASO or saline.

CONCLUSIONS

This study documents the first specific therapy, to our knowledge, for lowering apo(a)/Lp(a) levels and their associated OxPL. A more potent effect was documented in mice expressing apo(a) with multiple KIV-2 repeats. Targeting liver expression of apo(a) with ASOs directed to KIV-2 repeats may provide an effective approach to lower elevated Lp(a) levels in humans.

Cell type-specific regulation of IL-10 expression in inflammation and disease

IL-10 plays an essential part in controlling inflammation and instructing adaptive immune responses. Consequently, dysregulation of IL-10 is linked with susceptibility to numerous infectious and autoimmune diseases in mouse models and in humans. It has become increasingly clear that appropriate temporal/spatial expression of IL-10 may be the key to how IL-10 contributes to the delicate balance between inflammation and immunoregulation. The mechanisms that govern the cell type- and receptor-specific induction of IL-10, however, remain unclear. This is due largely to the wide distribution of cellular sources that express IL-10 under diverse stimulation conditions and in a variety of tissue compartments. Further complicating the issue is the fact that human IL-10 expression patterns appear to be under genetic influence resulting in differential expression and disease susceptibility. In this review, we discuss the cellular sources of IL-10, their link to disease phenotypes and the molecular mechanisms implicated in IL-10 regulation.

Lipoprotein(a) accelerates atherosclerosis in uremic mice

Uremic patients have increased plasma lipoprotein(a) [Lp(a)] levels and elevated risk of cardiovascular disease. Lp(a) is a subfraction of LDL, where apolipoprotein(a) [apo(a)] is disulfide bound to apolipoprotein B-100 (apoB). Lp(a) binds oxidized phospholipids (OxPL), and uremia increases lipoprotein-associated OxPL. Thus, Lp(a) may be particularly atherogenic in a uremic setting. We therefore investigated whether transgenic (Tg) expression of human Lp(a) increases atherosclerosis in uremic mice. Moderate uremia was induced by 5/6 nephrectomy (NX) in Tg mice with expression of human apo(a) (n = 19), human apoB-100 (n = 20), or human apo(a) + human apoB [Lp(a)] (n = 15), and in wild-type (WT) controls (n = 21). The uremic mice received a high-fat diet, and aortic atherosclerosis was examined 35 weeks later. LDL-cholesterol was increased in apoB-Tg and Lp(a)-Tg mice, but it was normal in apo(a)-Tg and WT mice. Uremia did not result in increased plasma apo(a) or Lp(a). Mean atherosclerotic plaque area in the aortic root was increased 1.8-fold in apo(a)-Tg (P = 0.025) and 3.3-fold (P = 0.0001) in Lp(a)-Tg mice compared with WT mice. Plasma OxPL, as detected with the E06 antibody, was associated with both apo(a) and Lp(a). In conclusion, expression of apo(a) or Lp(a) increased uremia-induced atherosclerosis. Binding of OxPL on apo(a) and Lp(a) may contribute to the atherogenicity of Lp(a) in uremia.

A human IL10 BAC transgene reveals tissue-specific control of IL-10 expression and alters disease outcome

Interleukin (IL)-10 is an immunoregulatory cytokine that is produced by diverse cell populations. Studies in mice suggest that the cellular source of IL-10 is a key determinant in various disease pathologies, yet little is known regarding the control of tissue-specific human IL-10 expression. To assess cell type-specific human IL-10 regulation, we created a human IL-10 transgenic mouse with a bacterial artificial chromosome (hIL10BAC) in which the IL10 gene is positioned centrally. Since human IL-10 is biologically active in the mouse, we could examine the in vivo capacity of tissue-specific human IL-10 expression to recapitulate IL-10-dependent phenotypes by reconstituting Il10(-/-) mice (Il10(-/-)/hIL10BAC). In response to LPS, Il10(-/-)/hIL10BAC mice proficiently regulate IL-10-target genes and normalize sensitivity to LPS toxicity via faithful human IL-10 expression from macrophages and dendritic cells. However, in the Leishmania donovani model of pathogen persistence, Il10(-/-)/hIL10BAC mice did not develop the characteristic IL-10(+)IFN-gamma(+)CD4 T cell subset thought to mediate persistence and, like Il10(-/-) mice, cleared the parasites. Furthermore, the IL-10-promoting cytokine IL-27 failed to regulate transgenic human IL-10 production in CD4(+) T cells in vitro which together suggests that the hIL10BAC encodes for weak T cell-specific IL-10 expression. Thus, the hIL10BAC mouse is a model of human gene structure and function revealing tissue-specific regulatory requirements for IL-10 expression which impacts disease outcomes.

Asymmetrical distribution of non-conserved regulatory sequences at PHOX2B is reflected at the ENCODE loci and illuminates a possible genome-wide trend

BACKGROUND

Transcriptional regulatory elements are central to development and interspecific phenotypic variation. Current regulatory element prediction tools rely heavily upon conservation for prediction of putative elements. Recent in vitro observations from the ENCODE project combined with in vivo analyses at the zebrafish phox2b locus suggests that a significant fraction of regulatory elements may fall below commonly applied metrics of conservation. We propose to explore these observations in vivo at the human PHOX2B locus, and also evaluate the potential evidence for genome-wide applicability of these observations through a novel analysis of extant data.

RESULTS

Transposon-based transgenic analysis utilizing a tiling path proximal to human PHOX2B in zebrafish recapitulates the observations at the zebrafish phox2b locus of both conserved and non-conserved regulatory elements. Analysis of human sequences conserved with previously identified zebrafish phox2b regulatory elements demonstrates that the orthologous sequences exhibit overlapping regulatory control. Additionally, analysis of non-conserved sequences scattered over 135 kb 5' to PHOX2B, provides evidence of non-conserved regulatory elements positively biased with close proximity to the gene. Furthermore, we provide a novel analysis of data from the ENCODE project, finding a non-uniform distribution of regulatory elements consistent with our in vivo observations at PHOX2B. These observations remain largely unchanged when one accounts for the sequence repeat content of the assayed intervals, when the intervals are sub-classified by biological role (developmental versus non-developmental), or by gene density (gene desert versus non-gene desert).

CONCLUSION

While regulatory elements frequently display evidence of evolutionary conservation, a fraction appears to be undetected by current metrics of conservation. In vivo observations at the PHOX2B locus, supported by our analyses of in vitro data from the ENCODE project, suggest that the risk of excluding non-conserved sequences in a search for regulatory elements may decrease as distance from the gene increases. Our data combined with the ENCODE data suggests that this may represent a genome wide trend.

Metrics of sequence constraint overlook regulatory sequences in an exhaustive analysis at phox2b

Despite its recognized utility, the extent to which evolutionary sequence conservation-based approaches may systematically overlook functional noncoding sequences remains unclear. We have tiled across sequence encompassing the zebrafish phox2b gene, ultimately evaluating 48 amplicons corresponding to all noncoding sequences therein for enhancer activity in zebrafish. Post hoc analyses of this interval utilizing five commonly used measures of evolutionary constraint (AVID, MLAGAN, SLAGAN, phastCons, WebMCS) demonstrate that each systematically overlooks regulatory sequences. These established algorithms detected only 29%-61% of our identified regulatory elements, consistent with the suggestion that many regulatory sequences may not be readily detected by metrics of sequence constraint. However, we were able to discriminate functional from nonfunctional sequences based upon GC composition and identified position weight matrices (PWM), demonstrating that, in at least one case, deleting sequences containing a subset of these PWMs from one identified regulatory element abrogated its regulatory function. Collectively, these data demonstrate that the noncoding functional component of vertebrate genomes may far exceed estimates predicated on evolutionary constraint.

Lipoprotein(a), lipids and proinflammatory cytokines in patients undergoing major abdominal surgery

Background

The aims were to investigate whether surgical stress can induce a positive or negative lipoprotein(a) acute response, to determine any association with apolipoprotein(a) phenotypes, and to establish whether any such response is dependent on changes in lipids and proinflammatory cytokines. In addition, the impact of interleukin (IL) 6 genetic variability on the cytokine response to surgery was examined.

Methods

This prospective, observational study included 41 patients with cancer referred for abdominal surgery. Preoperative (T0) plasma concentrations of lipoprotein(a), IL-6, tumour necrosis factor α, and serum concentrations of transforming growth factor β1 and lipids, were compared with values obtained 5 h (T1), 24 h (T2) and 5 days (T3) after surgery. Apolipoprotein(a) Kringle IV (KIV)-VNTR (variable-number tandem repeat) and IL-6 − 174 G/C polymorphisms were analysed.

Results

Lipoprotein(a) was found to act as a negative acute-phase reactant (30·0 per cent reduction at T2) (P = 0·009). Surgery had a more profound impact on subjects with low KIV-VNTR. After surgery, lipoprotein(a) correlated significantly with corrected low-density lipoprotein (LDL)-cholesterol (r = 0·408 at T2). IL-6 inversely correlated with lipoprotein(a) (r = −0·321 at T1) and LDL-cholesterol (r = −0·418 at T1). The IL-6 response could be predicted from a combination of the surgical severity and −174 G/C genotype.

Conclusion

Although temporal associations did not indicate causality, these data provide a hypothesis to explain the inverse relationship between lipoprotein(a) and IL-6.

Reduced LPA expression after peroxisome proliferator-activated receptor alpha (PPARα) activation in LPA-YAC transgenic mice

BACKGROUND:: Apolipoprotein(a) (apo(a)), which is part of the atherogenic lipoprotein Lp(a), shares structural homology with plasminogen (plg). Genes coding for plasminogen (PLG) and apo(a) (LPA) are linked and situated 40kb apart in the telomeric region of the long arm of chromosome 6. LPA is naturally expressed only in primates and hedgehogs. Thus, access to knowledge regarding the mechanism by which LPA expression is regulated is limited due to shortage of appropriate animal models. However, mice transgenic for the human LPA gene have been produced. Lp(a) levels in man are genetically determined and not altered significantly by dietary changes. In contrast, mice transgenic for LPA-yeast artificial chromosome (LPA-YAC) have markedly reduced apo(a) levels after maintenance on a high-fat diet. LPA-YAC carries the 40kb LPA-PLG intergenic region, which includes a putative binding site for peroxisome proliferator-activated receptor alpha (PPARalpha). Therefore, we examined if fibrates, which exert their effect via PPARalpha, could alter LPA expression in transgenic mice. METHODS:: Two LPA transgenic mouse lines with or without the LPA-PLG intergenic region we fed either PPARalpha agonist fenofibrate (FF) or 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (WY 14643) containing diets for 3 weeks. For the study of serum apo(a) levels, blood were sampled prior the experiment and when the animals were sacrificed. For the study of gene expression pattern pieces of livers were collected and submerged in RNAlater buffer and stored at -70 degrees C until analysis by quantitative PCR. RESULTS AND CONCLUSIONS:: The results showed that fibrates reduce LPA expression in LPA-YAC transgenic mice, but have no impact on hepatic apo(a) mRNA or serum apo(a) protein levels in LPA-cDNA transgenic mice, which lack the LPA-PLG intergenic region. This suggests that the effect of fibrates on LPA expression is mediated upstream of the LPA gene. However, on the basis of current data it is not possible to conclude that PPARalpha is the primary factor that represses LPA expression in LPA-YAC transgenic mice. Negative correlation between FXR and apo(a) mRNA levels, in addition to putative FXR DNA binding sequence in LPA-PLG intergenic region, suggest that it is equally likely that reduced expression of LPA could be a secondary consequence of PPARalpha activation on other genes, such as FXR.

Lipoprotein(a) as a risk factor for atherosclerosis and thrombosis: mechanistic insights from animal models

Evidence continues to accumulate from epidemiological studies that elevated plasma concentrations of lipoprotein(a) [Lp(a)] are a risk factor for a variety of atherosclerotic and thrombotic disorders. Lp(a) is a unique lipoprotein particle consisting of a moiety identical to low-density lipoprotein to which the glycoprotein apolipoprotein(a) [apo(a)] that is homologous to plasminogen is covalently attached. These features have suggested that Lp(a) may contribute to both proatherogenic and prothrombotic/antifibrinolytic processes and in vitro studies have identified many such candidate mechanisms. Despite intensive research, however, definition of the molecular mechanisms underlying the epidemiological data has proven elusive. Moreover, an effective and well-tolerated regimen to lower Lp(a) levels has yet to be developed. The use of animal models holds great promise for resolving these questions. Establishment of animal models for Lp(a) has been hampered by the absence of this lipoprotein from common small laboratory animals. Transgenic mice and rabbits expressing human apo(a) have been developed and these have been used to: (i) examine regulation of apo(a) gene expression; (ii) study the mechanism and molecular determinants of Lp(a) assembly from LDL and apo(a); (iii) demonstrate that apo(a)/Lp(a) are indeed proatherogenic and antifibrinolytic; and (iv) identify structural domains in apo(a) that mediate its pathogenic effects. The recent construction of transgenic apo(a) rabbits is a particularly promising development in view of the excellent utility of the rabbit as a model of advanced atherosclerosis.

Atherogenesis and vascular calcification in mice expressing the human LPA gene

Background: Lp(a) lipoprotein (Lp(a)) contains polymorphic glycoprotein, apolipoprotein(a) (apo(a)) and low density lipoprotein (LDL). The extensive homology between apo(a) and plasminogen is believed to contribute to the pathogenicity of apo(a), but the precise mechanisms by which Lp(a) participates in atherogenesis is still unknown. We used LPA-yeast artificial chromosome (LPA-YAC) transgenic mice with or without the human APOB (hAPOB) gene to study pathogenicity of apo(a)/Lp(a) and illucidate its role in regulation of serum lipid levels. Methods: Middle-aged (1-year-old) mice were fed a control (AIN-76), a high-cholesterol (HC) or a high-cholesterol/high-fat (HCHF) diet for 7 weeks. For the study of serum total apo(a) and lipid levels, mice were sampled prior to the experiment, at 2 weeks and at 7 weeks when the animals were sacrificed. Hearts with ascending aorta were fixed in formalin, embedded in gelatine and prepared for sections on a cryostat. Livers were washed in ice cold saline and submerged in RNAlater trade mark buffer and stored at -70 degrees C until mRNA analysis. Results: Wild type mice fed the control diet did not develop aortic lesions. Presence of the LPA gene was sufficient to induce development of aortic lesions, but neither coexpression of the hAPOB gene nor feeding the HC diet or the HCHF diet augmented the development of aortic lesions in LPA-YAC transgenic mice. On the control diet transgenic females had larger aortic lesion size than transgenic males. Furthermore, aortic lesions in transgenic females were associated with calcification more often than in transgenic males. Serum total cholesterol levels were higher both in wild type and LPA-YAC transgenic males than in females mainly because of higher serum high-density lipoprotein cholesterol levels. HC and HCHF feeding had more pronounced effect on total cholesterol levels in LPA-YAC/hAPOB transgenic mice than in either wild type or LPA-YAC transgenic mice, due to increased low density lipoprotein cholesterol levels. Furthermore, these diets reduced serum total apo(a) levels in both transgenic mouse lines. Conclusion: Expression of the human LPA gene in mice is sufficient to trigger development of aortic lesions. Similar frequency of calcified lesions in LPA-YAC transgenic mice with or without hAPOB gene may suggest that apo(a) is the part of the Lp(a) molecule that causes aortic calcification. The basis for reduced serum total apo(a) level in response to cholesterol feeding is not clear, but interplay between LPA and factors involved in cholesterol or bile acid homeostasis is worth of future studies.

A glucose response element from the S. cerevisiae hexose transporter HXT1 gene is sensitive to glucose in human fibroblasts

Glucose is an essential nutrient, and a regulator of gene expression in eukaryotic cells. Here, a comparative, function-based genomic approach has been used to identify glucose regulatory elements and transduction pathways common to both yeast and mammalian cells. We have isolated a region in the promoter of the Saccharomyces cerevisiae hexose transporter gene HXT1 that conferred glucose sensitivity in yeast, when located upstream of the minimal CYC1 promoter. This element contained binding motifs for Rgt1, a transcriptional modulator involved in the yeast glucose-induction pathway, that were sufficient to elicit glucose responsiveness. The HXT1 regulatory element was then fused to the minimal cytomegalovirus promoter (HXT1-MIN) and inserted into an adenovirus for delivery to human fibroblasts, where it exhibited glucose-dependent transcriptional activation. Glucose action was mimicked by fructose and unrelated to glucose 6-P content, whilst non-metabolizable glucose analogues showed no effect. Activation of AMP kinase by 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranosanide blocked glucose induction, revealing parallels with the yeast glucose-repressing pathway. In contrast, delivery of Rgt1 to fibroblasts did not modify HXT1-MIN responsiveness. Thus, elements of the S.cerevisiae HXT1 gene conserve glucose regulation in human fibroblasts equivalent to the metabolism-dependent, glucose-repressing pathway in yeast. These data suggest that the instructions carried within gene regulatory elements controlling nutrient regulation of gene expression have been conserved throughout evolution.

Human apoB contributes to increased serum total apo(a) level in LPA transgenic mice

Background

The Lp(a) lipoprotein (Lp(a)) consists of the polymorphic glycoprotein apolipoprotein(a) (apo(a)), which is attached by a disulfide bond to apolipoprotein B (apoB). Apo(a), which has high homology with plasminogen, is present only in primates and hedgehogs. However, transgenic mice and rabbits with high serum apo(a) levels exist. Liver is the main site for apo(a) synthesis, but the site of removal is uncertain. To examine differences between transgenic mice expressing the LPA gene and mice capable of forming Lp(a) particles, LPA-YAC transgenic mice and hAPOB transgenic mice were crossed and their offspring examined.

Results

Comparison of LPA-YAC with LPA-YAC/hAPOB transgenic mice showed that LPA-YAC/hAPOB transgenic mice have higher serum total apo(a) and total cholesterol level than mice lacking the hAPOB gene. However, hepatic apo(a) mRNA level was higher in LPA-YAC transgenic mice than in LPA-YAC/hAPOB transgenic mice. Feeding of a high-cholesterol/high-fat diet to male LPA-YAC transgenic mice with or without the hAPOB gene resulted in reduced serum total apo(a) and hepatic apo(a) mRNA level.

Conclusion

In conclusion, the higher serum total apo(a) level in LPA-YAC/hAPOB transgenic mice than in LPA-YAC transgenic mice is not caused by increased apo(a) synthesis. Lower hepatic apo(a) mRNA level in LPA-YAC/hAPOB than in LPA-YAC transgenic mice may suggest that the increase in total apo(a) level is a result of apo(a) accumulation in serum. Furthermore, observed higher serum total cholesterol level in LPA-YAC/hAPOB transgenic mice than either in wild type or LPA-YAC transgenic mice may further suggest that human APOB transgenicity is a factor that contributes to increased serum total apo(a) and cholesterol levels. Our results on reduced serum total apo(a) and hepatic apo(a) mRNA levels in HCHF fed male LPA-YAC transgenic mice confirm earlier findings in females, and show that there are no sex difference in mechanisms for lowering apo(a) level in response to HCHF feeding.

Lipoprotein (a) and acute-phase response in patients with vestibular neuronitis

BACKGROUND

Vestibular neuronitis (VN) is a relatively common condition characterized by the acute onset of vertigo, nausea and vomiting, in the absence of auditory or central nervous system involvement. The exact aetiology (inflammatory, viral or vascular?) remains obscure. Lipoprotein (a) [Lp(a)] is an atherogenic particle. Its serum levels are mainly genetically determined and vary widely between individuals. Whether Lp(a) is consistently a positive acute-phase reactant is controversial.

PURPOSE

We evaluated the alterations in lipidaemic parameters and serum biological markers (including acute-phase reactants) in adult patients presenting acutely with VN.

SUBJECTS AND METHODS

A total of 34 consecutive VN patients (24 men and 11 women) and 37 apparently healthy controls (25 men and 12 women) were studied. Laboratory evaluation was performed during the acute episode and 6 months later (stable state).

RESULTS

Serum Lp(a) concentrations were significantly lower at the time of presentation (median value 6.4 vs. 16.4 mg dL-1 in the stable state, P < 0.001), whereas fibrinogen levels were significantly higher during the acute episode than in the stable state (median value 293.0 vs. 202.0 mg dL-1, respectively, P < 0.0001). During the acute episode, plasma fibrinogen correlated with CRP levels (Spearman r = 0.84, P < 0.0001). By contrast, inverse correlations were noted between Lp(a) levels and CRP (Spearman r = -0.47, P = 0.007) as well as between Lp(a) and fibrinogen levels (Spearman r = -0.35, P = 0.05).

CONCLUSION

Vestibular neuronitis episodes are associated with evidence of an acute inflammatory response as reflected by significant elevations in plasma fibrinogen and CRP concentrations, whereas Lp(a) behaves as a negative acute-phase reactant.

Estrogen agonists/antagonists may down-regulate growth hormone signaling in hepatocytes--an explanation for their impact on IGF-I, IGFBP-1, and lipoprotein(a)

Estrogen agonists/antagonists, when administered orally, exert a range of effects on hepatic function, some of which are potentially protective. These effects include reduced synthesis of IGF-I and apolipoprotein(a), and increased synthesis of IGFBP-1--shifts which arguably could decrease risk for vascular disease and certain cancers. These effects are diametrically opposite to those of growth hormone (GH), which boosts hepatic production of IGF-I and apolipoprotein(a), while suppressing that of IGFBP-1. Thus, a parsimonious explanation of these phenomena is that oral estrogen blunts the efficiency of GH signaling in the liver. Oral androgenic progestins may have the reverse effect. It may be of particular value to determine whether certain estrogen agonists/antagonists can exert relatively 'hepatospecific' activity when administered orally--thus enabling down-regulation of systemic IGF-I activity and of lipoprotein(a), without however inducing a significant increase in systemic estrogen activity. Preliminary evidence suggests that flax lignans and perhaps other phytoestrogens may have potential in this regard.

Regulation of the expression of the apolipoprotein(a) gene: evidence for a regulatory role of the 5' distal apolipoprotein(a) transcription control region enhancer in yeast artificial chromosome transgenic mice

OBJECTIVE

The apolipoprotein(a) [apo(a)] gene locus is the major determinant of the circulating concentration of the atherothrombogenic lipoprotein Lp(a). In vitro analysis of the intergenic region between the apo(a) and plasminogen genes revealed the presence of a putative apo(a) transcription control region (ACR) approximately 20 kb upstream of the apo(a) gene that significantly increases the minimal promoter activity of the human apo(a) gene.

METHODS AND RESULTS

To examine the function of the ACR in its natural genomic context, we used the Cre-loxP recombination system to generate 2 nearly identical apo(a)-yeast artificial chromosome transgenic mouse lines that possess a single integration site for the human apo(a) transgene in the mouse genome but differ by the presence or absence of the ACR enhancer. Analysis of the 2 groups of animals revealed that the deletion of the ACR was associated with 30% reduction in plasma and mRNA apo(a) levels. Apo(a)-yeast artificial chromosome transgenic mice with and without the ACR sequence were similar in all other aspects of apo(a) regulation, including liver-specific apo(a) expression and alteration in expression levels in response to sexual maturation and a high-fat diet.

CONCLUSIONS

This study provides the first experimental in vivo evidence for a functional role of the ACR enhancer in determining levels of apo(a) expression.

Genomic studies of gene expression: regulation of the Wilson disease gene

Bacterial artificial chromosomes (BACs) have many advantages over other large-insert cloning vectors and have been used for a variety of genetic applications, including the final contigs of the human genome. We describe the utilization of a BAC construct to study gene regulation in a tissue culture-based system, using a 170-kb clone containing the entire Wilson disease (WND) locus as a model. A second BAC construct that lacked a putative negatively regulating promoter sequence was created. A nonviral method of gene delivery was applied to transfect three human cell lines stably with each construct. Our results show correct WND gene expression from the recombinant locus and quantification revealed significantly increased expression from the clone lacking the negative regulator. Comparison with conventional methods confirms the reliability of the genomic approach for thorough examination of gene expression. This experimental system illustrates the potential of BAC clones in genomic gene expression studies, new gene therapy strategies, and validation of potential molecular targets for drug discovery.

Androgens and coronary artery disease

A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low high-density lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease.

Cardiovascular effects of androgens

In the process of atherosclerosis sex steroids play a complex role in the vascular vessel wall system. Although a number of experimental studies have clearly documented an atheroprotective effect of estrogens, in recent clinical studies, estrogen replacement therapy has failed to reduce cardiovascular mortality. The effects of androgens on the cardiovascular system and cardiovascular diseases are even more controversial. Whereas in the past, androgens were mainly believed to exert adverse effects on the cardiovascular system, recent studies in men have documented a number of beneficial actions of testosterone in the arterial vascular system. Androgens affect lipid metabolism (e.g., LDL and HDL cholesterol, Lp(a)) and hemostasis (e.g., platelet aggregation and fibrinolytic activity). In addition, several other physiological and pathophysiological processes in the arterial vessel wall are influenced by androgens. Acute hemodynamic effects of testosterone on coronary vasomotion and stress-test-induced ischemia were reported. Additionally, recent animal and in vitro studies have further documented an inhibitory effect of androgens on neointimal plaque formation. This review discusses different and, in part, contradictory effects of androgens on the cardiovascular system including potential signal transduction pathways in androgen target cells.

Interaction of oestrogen and peroxisome proliferator-activated receptors with apolipoprotein(a) gene enhancers

A high plasma concentration of lipoprotein(a) [Lp(a)] confers an increased risk for the development of coronary heart disease. Hormones, such as oestrogen, are some of the few compounds known to reduce plasma Lp(a) levels. A putative enhancer region, located at the DHII DNase I hypersensitive site approx. 28 kb upstream of the apolipoprotein(a) [apo(a)] gene, contains a number of sequences similar to the binding half-sites for nuclear hormone receptors, such as the oestrogen receptor and the peroxisome proliferator-activated receptor (PPAR). The 180 bp core DHII enhancer increased the activity of the apo(a) promoter by over 7-fold in reporter-gene assays in HepG2 cells in vitro. Almost 60% of this increase was lost in the presence of co-transfected oestrogen receptor and oestrogen. In contrast, co-transfection with PPARalpha increased the effect of the DHII enhancer on apo(a) transcriptional activity by approx. 70% and could overcome the inhibitory effect of the oestrogen receptor on apo(a) transcription. Gel mobility-shift assays showed that oestrogen receptor protein bound to one half of a sequence corresponding to a predicted oestrogen receptor response element. PPARalpha also bound to this site and competed with oestrogen receptors for binding. In addition, PPARalpha bound to a separate site that comprised part of a direct repeat of nuclear hormone receptor half-sites. The results suggest that nuclear hormones affect plasma Lp(a) concentrations by binding to the sequences within the DHII enhancer, thereby altering the amount by which the enhancer increases the transcription of the apo(a) gene.

Lipoprotein(a) promotes smooth muscle cell proliferation and dedifferentiation in atherosclerotic lesions of human apo(a) transgenic rabbits

Elevated plasma lipoprotein(a) [Lp(a)] levels constitute an independent risk factor for the development of atherosclerosis. However, the mechanism underlying Lp(a) atherogenicity is unclear. Recently, we demonstrated that Lp(a) may potentially be proatherogenic in transgenic rabbits expressing human apolipoprotein(a) [apo(a)]. In this study, we further investigated atherosclerotic lesions of transgenic rabbits by morphometry and immunohistochemistry. On a cholesterol diet, human apo(a) transgenic rabbits had more extensive atherosclerotic lesions of the aorta, carotid artery, iliac artery, and coronary artery than did nontransgenic littermate rabbits as defined by increased intimal lesion area. Enhanced lesion development in transgenic rabbits was characterized by increased accumulation of smooth muscle cells, that was often associated with the Lp(a) deposition. To explore the possibility that Lp(a) may be involved in the smooth-muscle cell phenotypic modulation, we stained the lesions using a panel of monoclonal antibodies against smooth-muscle myosin heavy-chain isoforms (SM1, SM2, and SMemb) and basic transcriptional element binding protein-2 (BTEB2). We found that a large number of smooth muscle cells located in the apo(a)-containing areas of transgenic rabbits were positive for SMemb and BTEB2, suggesting that these smooth muscle cells were either immature or in the state of activation. In addition, transgenic rabbits showed delayed fibrinolytic activity accompanied by increased plasma plasminogen activator inhibitor-1. We conclude that Lp(a) may enhance the lesion development by mediating smooth muscle cell proliferation and dedifferentiation possibly because of impaired fibrinolytic activity.

Of mice and genome sequence

Availability of the mouse genome sequence will have a major impact on the study of vertebrate evolution, mammalian biology, and animal models of human disease. Resources to explore genome biology in mice will maximize the effect of this watershed event.

An apolipoprotein influencing triglycerides in humans and mice revealed by comparative sequencing

Comparison of genomic DNA sequences from human and mouse revealed a new apolipoprotein (APO) gene (APOAV) located proximal to the well-characterized APOAI/CIII/AIV gene cluster on human 11q23. Mice expressing a human APOAV transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoav had four times as much plasma triglycerides as controls. In humans, single nucleotide polymorphisms (SNPs) across the APOAV locus were found to be significantly associated with plasma triglyceride levels in two independent studies. These findings indicate that APOAV is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.

Transgenic rabbits expressing human apolipoprotein (a)

Elevated plasma levels of lipoprotein (a) [Lp(a)] constitutes an independent risk factor for coronary heart disease, stroke, and restenosis. Over the past years, our understanding of the genetics, metabolism and pathophysiology of Lp(a) have increased considerably. However, the precise mechanism(s) by which this atherogenic lipoprotein mediates the development of atherosclerosis remains unclear. This is partly due to the lack of appropriate animal models since apolipoprotein (a) [apo(a)], a distinct component of Lp(a) is found only in primates and humans. Development of transgenic mice expressing human apo(a) has provided an alternative means to investigate many aspects of Lp(a). However, human apo(a) in transgenic mice can not bind to murine apoB to form Lp(a) particles. In this aspect, we generated transgenic rabbits expressing human apo(a). In the plasma of transgenic rabbits, unlike the plasma of transgenic mice, about 80% of the apo(a) was associated with rabbit apo B and was contained in the fractions with density 1.02-1.10 g/ml, indicating the formation of Lp(a). Our study suggests that transgenic rabbits expressing human apo(a) exhibit efficient assembly of Lp(a) and can be used as an animal model for the study of human Lp(a).

Human chromosome 19 and related regions in mouse: conservative and lineage-specific evolution

To illuminate the function and evolutionary history of both genomes, we sequenced mouse DNA related to human chromosome 19. Comparative sequence alignments yielded confirmatory evidence for hypothetical genes and identified exons, regulatory elements, and candidate genes that were missed by other predictive methods. Chromosome-wide comparisons revealed a difference between single-copy HSA19 genes, which are overwhelmingly conserved in mouse, and genes residing in tandem familial clusters, which differ extensively in number, coding capacity, and organization between the two species. Finally, we sequenced breakpoints of all 15 evolutionary rearrangements, providing a view of the forces that drive chromosome evolution in mammals.

Effects of hormone replacement on hemostasis in spontaneous menopause

OBJECTIVE

To examine the effects of continuous combined estrogen-progesterone replacement therapy on coagulation and natural anticoagulant systems in spontaneous menopause.

DESIGN

A randomized, double-blind, placebo-controlled study was conducted during a 6-month period to examine the effect of hormone replacement therapy (HRT) on blood coagulation parameters. One hundred-ten healthy postmenopausal women were randomized into two groups. Those in group 1 were given conjugated estrogen (0.625 mg/d, Premarin) and medroxyprogesterone acetate (5 mg/d, Farlutal), and those in group 2 were given identical tablets of placebo for 6 months. Serum levels of modified activated protein C resistance, antithrombin III, fibrinogen, factor VIIIa, factor VIII, factor IX, activated partial thromboplastin time, prothrombin time, thrombin time, and lipoprotein (a) were measured before and 6 months after the treatment and analyzed for changes in extrinsic and intrinsic coagulation parameters.

RESULTS

At the end of the 6-month period, fibrinogen, lipoprotein (a), and activated protein C resistance levels were decreased significantly in the HRT group compared with the control group. Antithrombin III levels were increased, indicating antithrombin activity. Activated partial thromboplastin time, as a measure for intrinsic coagulation cascade, was prolonged in concert with decreased intrinsic coagulation factors, factor VIII, and factor IX (p < 0.05). In the extrinsic coagulation system, prothrombin time was significantly increased, although factor VIIa level was not changed (p > 0.05).

CONCLUSION

Significant changes were observed in the coagulation parameters, which may further explain the cardioprotective effect of HRT.

Size matters: use of YACs, BACs and PACs in transgenic animals

In 1993, several groups, working independently, reported the successful generation of transgenic mice with yeast artificial chromosomes (YACs) using standard techniques. The transfer of these large fragments of cloned genomic DNA correlated with optimal expression levels of the transgenes, irrespective of their location in the host genome. Thereafter, other groups confirmed the advantages of YAC transgenesis and position-independent and copy number-dependent transgene expression were demonstrated in most cases. The transfer of YACs to the germ line of mice has become popular in many transgenic facilities to guarantee faithful expression of transgenes. This technique was rapidly exported to livestock and soon transgenic rabbits, pigs and other mammals were produced with YACs. Transgenic animals were also produced with bacterial or P1-derived artificial chromosomes (BACs/PACs) with similar success. The use of YACs, BACs and PACs in transgenesis has allowed the discovery of new genes by complementation of mutations, the identification of key regulatory sequences within genomic loci that are crucial for the proper expression of genes and the design of improved animal models of human genetic diseases. Transgenesis with artificial chromosomes has proven useful in a variety of biological, medical and biotechnological applications and is considered a major breakthrough in the generation of transgenic animals. In this report, we will review the recent history of YAC/BAC/PAC-transgenic animals indicating their benefits and the potential problems associated with them. In this new era of genomics, the generation and analysis of transgenic animals carrying artificial chromosome-type transgenes will be fundamental to functionally identify and understand the role of new genes, included within large pieces of genomes, by direct complementation of mutations or by observation of their phenotypic consequences.

Genomic strategies to identify mammalian regulatory sequences

With the continuing accomplishments of the human genome project, high-throughput strategies to identify DNA sequences that are important in mammalian gene regulation are becoming increasingly feasible. In contrast to the historic, labour-intensive, wet-laboratory methods for identifying regulatory sequences, many modern approaches are heavily focused on the computational analysis of large genomic data sets. Data from inter-species genomic sequence comparisons and genome-wide expression profiling, integrated with various computational tools, are poised to contribute to the decoding of genomic sequence and to the identification of those sequences that orchestrate gene regulation. In this review, we highlight several genomic approaches that are being used to identify regulatory sequences in mammalian genomes.

Transgenic rabbits expressing human apolipoprotein(a) develop more extensive atherosclerotic lesions in response to a cholesterol-rich diet

High lipoprotein(a) [Lp(a)] levels constitute an independent risk factor for the development of atherosclerosis. However, the relationship between Lp(a) and atherosclerosis is not fully understood. To examine the effect of Lp(a) on the development of atherosclerosis, we studied transgenic rabbits expressing human apolipoprotein(a) [apo(a)], which was assembled into Lp(a) in the plasma. Human apo(a) transgenic rabbits fed a 0.3% cholesterol diet for 16 weeks had more extensive atherosclerotic lesions than did nontransgenic rabbits, although the cholesterol levels in the plasma of both groups were similarly elevated. Compared with the lesions in control rabbits, the areas of the atherosclerotic lesions in human apo(a) transgenic rabbits were significantly increased in the aorta, the iliac artery, and the carotid artery. Furthermore, human apo(a) transgenic rabbits on a cholesterol-rich diet had a greater degree of coronary atherosclerosis than did control rabbits. Immunohistochemical analysis revealed that human apo(a) was frequently deposited in the atherosclerotic lesions of transgenic rabbits. We conclude that Lp(a) may have proatherogenic effects in the setting of a cholesterol-rich diet in transgenic rabbits.

Up-regulation of I-2(PP2A)/SET gene expression in rat primary hepatomas and regenerating livers

I-2(PP2A)/SET, an inhibitor of protein phosphatase 2A, is supposed to be one of the oncoproteins associated with human myeloid leukemia. The I-2(PP2A)/SET gene expression was observed ubiquitously among all the rat tissues examined, but low in liver. Of interest is that the expression in the rat primary hepatomas and hyperplastic nodules was significantly elevated. The experiments using regenerating livers after partial hepatectomy showed that the expression of I-2(PP2A)/SET mRNA was low at the quiescent hepatocytes, but up-regulated at 12-24 h after partial hepatectomy, which corresponds to the mid G1 to S transition in the cell cycle. These results suggested the importance of I-2(PP2A)/SET in the hepatocarcinogenesis and hepatic cell proliferation.

Single-step conversion of P1 and P1 artificial chromosome clones into yeast artificial chromosomes

Large insert genomic clones are useful for generating transgenic animals, particularly when specific mutations are introduced. To facilitate manipulation of large genomic sequences, we developed a method of converting Escherichia coli P1 artificial chromosomes (PACs) into yeast artificial chromosomes (YACs). A shuttle vector, pMAX-121, was generated that contains elements needed to generate a YAC (cen4, ars, ura3, his, and two telomere segments) along with approximately 1.3 kb of sequence homologous to P1 and PAC vector sequences. Cotransformation of yeast with the target PAC or P1 clone and pMAX-121 results in two homologous recombination events. The first, between the target clone and pMAX-121, results in a circular molecule. The second is an intramolecular recombination event between the two pMAX-121 telomere sequences, resulting in a linear molecule. The resulting YAC is stably maintained in yeast and can be further modified using homologous recombination. The method was used to convert a 201-kb PAC containing the human tau gene into a stable linear YAC. A second vector, pLys2-neo, was developed to retrofit the YAC with the yeast lys2 gene, a selectable marker replacing the yeast ura3 gene, and a Pgk-neo cassette that confers G418 resistance to mammalian cells. The resulting YAC can be used for generating transgenic animals and stably transfected cell lines. Also, the lys2 marker facilitates introduction of mutations by homologous recombination.

Major reduction in plasma Lp(a) levels during sepsis and burns

Plasma levels of lipoprotein(a) [Lp(a)], an atherogenic particle, vary widely between individuals and are highly genetically determined. Whether Lp(a) is a positive acute-phase reactant is debated. The present study was designed to evaluate the impact of major inflammatory responses on plasma Lp(a) levels. Plasma levels of C-reactive protein (CRP), low density lipoprotein cholesterol, Lp(a), and apolipoprotein(a) [apo(a)] fragments, as well as urinary apo(a), were measured serially in 9 patients admitted to the intensive care unit for sepsis and 4 patients with extensive burns. Sepsis and burns elicited a major increase in plasma CRP levels. In both conditions, plasma concentrations of Lp(a) declined abruptly and transiently in parallel with plasma low density lipoprotein cholesterol levels and closely mirrored plasma CRP levels. In 5 survivors, the nadir of plasma Lp(a) levels was 5- to 15-fold lower than levels 16 to 18 months after the study period. No change in plasma levels of apo(a) fragments or urinary apo(a) was noticed during the study period. Turnover studies in mice indicated that clearance of Lp(a) was retarded in lipopolysaccharide-treated animals. Taken together, these data demonstrate that Lp(a) behaves as a negative acute-phase reactant during major inflammatory response. Nongenetic factors have a major, acute, and unexpected impact on Lp(a) metabolism in burns and sepsis. Identification of these factors may provide new tools to lower elevated plasma Lp(a) levels.