Elevated Expression of Phospholipid Transfer Protein in Bone Marrow Derived Cells Causes Atherosclerosis

Background: Phospholipid transfer protein (PLTP) is expressed by various cell types. In plasma, it is associated with high density lipoproteins (HDL). Elevated levels of PLTP in transgenic mice result in decreased HDL and increased atherosclerosis. PLTP is present in human atherosclerosis lesions, where it seems to be macrophage derived. The aim of the present study is to evaluate the atherogenic potential of macrophage derived PLTP. Methods and Findings: Here we show that macrophages from human PLTP transgenic mice secrete active PLTP. Subsequently, we performed bone marrow transplantations using either wild type mice (PLTPwt/wt), hemizygous PLTP transgenic mice (huPLTPtg/wt) or homozygous PLTP transgenic mice (huPLTPtg/tg) as donors and low density lipoprotein receptor deficient mice (LDLR-/-) as acceptors, in order to establish the role of PLTP expressed by bone marrow derived cells in diet-induced atherogenesis. Atherosclerosis was increased in the huPLTPtg/wt → LDLR-/ - mice (2.3-fold) and even further in the huPLTPtg/tg→LDLR-/ - mice (4.5-fold) compared with the control PLTPwt/wt→LDLR-/- mice (both P<0.001). Plasma PLTP activity levels and non-HDL cholesterol were increased and HDL cholesterol decreased compared with controls (all P<0.01). PLTP was present in atherosclerotic plaques in the mice as demonstrated by immunohistochemistry and appears to co-localize with macrophages. Isolated macrophages from PLTP transgenic mice do not show differences in cholesterol efflux or in cytokine production. Lipopolysaccharide activation of macrophages results in increased production of PLTP. This effect was strongly amplified in PLTP transgenic macrophages. Conclusions: We conclude that PLTP expression by bone marrow derived cells results in atherogenic effects on plasma lipids, increased PLTP activity, high local PLTP protein levels in the atherosclerotic lesions and increased atherosclerotic lesion size

The physiological role of lipoprotein (a)

Lipoprotein (a) (Lp(a)) is one of the most atherogenic lipoproteins, and, although we know plenty about the pathophysiology of Lp(a), its physiological function and metabolism remain elusive. From our previous results and more recent reports, the following model of Lp(a) metabolism emerges: apolipoprotein a (apo(a)) is biosynthesized in liver cells and the size of the isoform determines its rate of synthesis and excretion. In a first step, specific kringle IV domains in apo(a), mainly T-6 and T-7, bind to circulating low-density lipoproteins, followed by a second step in which stabilization of the newly formed Lip(a) complex is achieved by a disulfide bridge. Circulating Lp(a) interacts specifically with kidney cells, or possibly other tissues, causing cleavage of 2/3-3/4 of the N-terminal part of apo(a) by a collagenase-type protease. Part of these apo(a) fragments are found as excretory products of Lp(a) in urine, but there are indications that they, in fact, represent the biologically active form of apo(a) and are possibly responsible for the atherogenicity of Lp(a). Strategies for reducing this atherogenic lipoprotein with medication should, therefore, aim at interfering with either the assembly of Lp(a) or the stimulation of apo(a) fragmentation. (C) 2002 Prous Science, All rights reserved

Apolipoprotein E polymorphism is not associated with longevity or disability in a sample of Italian octo- and nonagenarians

BACKGROUND: Apolipoprotein E (apo E) is a protein associated with plasma lipoproteins. Apo E polymorphism has been related to significant modifications of lipoprotein profile, as well as to the incidence of different pathologies including cardiovascular disease, Alzheimer's disease, and vascular dementia. Furthermore, it was proposed that apo E polymorphism might be involved in the aging selection process. OBJECTIVE: The purposes of the present study were the following: (1) to evaluate apo E polymorphism in 'successful' and 'unsuccessful' aging, defined as the absence or presence of disability and severe chronic diseases (mainly cardiovascular disease and dementia), respectively; (2) to evaluate the impact of apo E polymorphism on plasma lipids in very old individuals free of or affected by disability. METHODS: 253 Italian subjects including 100 free-living healthy octo- and nonagenarians, 62 disabled octo- and nonagenarians, and 91 healthy adult controls, all matched for origin were studied. Apo E phenotypes were determined by PhastSystem (Pharmacia). Lipoprotein parameters (total cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol, lipoprotein (a), and apoprotein A-I and B) were measured by standardized methods. ADL were evaluated by the Katz index. RESULTS: The frequency of sigma2, sigma3, and sigma4 alleles was 0.062, 0.887, and 0.051 respectively in the entire sample; no differences in alleles distribution were found between the three groups. When the subjects were divided according to the E type (E2 type: E2/E2 and E2/E3; E3 type: E3/E3; E4 type: E3/E4 and E4/E4), no differences in lipoprotein parameters emerged, but a trend toward higher total and LDL-cholesterol from the E2 to the E4 type was observed. The sigma4 allele had a raising effect, while sigma2 had a lowering effect on total cholesterol levels, but these effects were much less profound in the disabled octo- and nonagenarians. CONCLUSIONS: We conclude that (1) the frequency of the sigma4 allele is very low in this sample of subjects from central Italy; (2) no differences emerged in sigma4 distribution between healthy and disabled octo- and nonagenarians, and adult controls; the very low frequency of sigma4 allele might contribute to this finding; (3) our data do not support the hypothesis of a possible association between apo E polymorphism and longevity or disability in this population

Urinary excretion of apolipoprotein(a): relation to other plasma proteins

The atherogenic lipoprotein Lp(a) consists of an LDL-like core and apo(a). linked to apoB via a thiol bridge. Apo(a) fragments ranging in size from 60 to 220 kDa are excreted into urine and the excretion rate correlates significantly with the plasma levels of Lp(a). In order to study the interrelationship of apo(a) secretion with that of other plasma proteins. urinary apo(a) and protein secretion of five probands were followed for 24 h at different urinary densities. The excretion rate of apo(a) fragments, despite their high molecular weight, was highest. followed by apoD. orosomucoid. albumin and beta (2)-glycoprotein-I (beta2-GI) and plasminogen (1.58, 0.87, 0.095, 0.027, 0.013 an