Three viral proteins participate in the down-modulation of CD4 in human immunodeficiency virus type 1 (HIV-1)-infected cells. The underlying mechanisms have been extensively investigated. However, the physiological relevance of this phenomenon remains poorly understood. To address the role of CD4 down-modulation in HIV-1 pathogenesis in vivo, we have characterized the functional properties of nef alleles isolated from seven HIV-1-infected patients at either the stage of AIDS (late alleles) or during the asymptomatic phase of infection (early alleles). HIV-1 variants carrying these nef alleles showed striking differences in CD4 down-modulation, virus infectivity, and replication properties. Infection of T cells with late strains resulted in production of viral particles with enhanced infectivity, as compared with variants carrying early nef alleles. These differences in infectivity were observed only when viruses were produced in cells with high levels of the viral receptor, suggesting a functional link between CD4 levels and the ability of Nef to down-modulate CD4 and to enhance viral infectivity. Similarly, late nef alleles were substantially more active than early nef genes in stimulating HIV-1 replication in high CD4-positive cells, including primary lymphocytes, but not in cells expressing low levels of the CD4 receptor. Single-round assays showed that differences in infectivity between late and early strains are largely reduced when evaluated in target cells with high levels of CD4, suggesting that the inhibitory effect occurs at the entry step. Supporting this, enhanced CD4 down-modulation by late nef alleles was associated with higher levels of envelope incorporation into viral particles, a phenomenon that likely accounted for the augmented infectivity. Our data suggest a mechanistic link between the Nef-mediated CD4 down-modulation and the enhancement of replication in CD4-positive lymphocytes. As progression to disease occurs, HIV-1 Nef variants with enhanced ability to down-modulate CD4 are selected. These strains efficiently overcome the deleterious effects of CD4 and replicate more aggressively in CD4-positive primary lymphocytes. These results highlight the importance of the virus-induced CD4 down-modulation in HIV-1 pathogenesis.

The CD4 protein is required for the entry of human immunodeficiency virus (HIV) into target cells. Upon expression of the viral genome, three HIV-1 gene products participate in the removal of the primary viral receptor from the cell surface. To investigate the role of surface-CD4 in HIV replication, we have created a set of Jurkat cell lines which constitutively express surface levels of CD4 comparable to those found in peripheral blood lymphocytes and monocytes. Expression of low levels of CD4 on the surface of producer cells exerted an inhibitory effect on the infectivity of HIV-1 particles, whereas no differences in the amount of cell-free p24 antigen were observed. Higher levels of cell surface CD4 exerted a stronger inhibitory effect on infectivity, and also affected the release of free virus in experiments where the viral genomes were delivered by electrotransfection. The CD4-mediated inhibition of HIV-1 infectivity was not observed in experiments where the vesicular stomatitis virus G protein was used to pseudotype viruses, suggesting that an interaction between CD4 and gp120 is required for interference. In contrast, inhibition of particle release by high levels of cell-surface CD4 was not overcome by pseudotyping HIV-1 with foreign envelope proteins. Protein analysis of viral particles released from HIV-infected Jurkat-T cells revealed a CD4-dependent reduction in the incorporation of gp120. These results demonstrate that physiological levels of cell-surface CD4 interfere with HIV-1 replication in T cells by a mechanism that inhibits envelope incorporation into viral membranes, and therefore provide an explanation for the need to down-modulate the viral receptor in infected cells. Our findings have important implications for the spread of HIV in vivo and suggest that the CD4 down-modulation function may be an alternative target for therapeutic intervention. HIV1 down-modulates its own receptor, the CD4 protein. Removal of CD4 from the surface of infected cells is achieved by the Nef, Vpu, and Env products (1-8). Nef acts early after infection by accelerating the internalization of CD4 and targeting it to late endosomes for degradation (6, 9 -13). Env and Vpu cooperate inside the cell to block the transport of CD4 to the cell surface and redirect this protein to the ubiquitin-proteosome machinery for degradation (1, 14 -16). The Env protein sequesters CD4 in the endoplasmic reticulum by an interaction mediated by the extracellular domains of CD4 and Env (8, 17), whereas Vpu induces the degradation of the HIV receptor by a mechanism which requires an interaction between the cytoplasmic tails of CD4 and Vpu (1,7,18,19). The fact that the combined action of three HIV-1 gene products is required for the nearly complete elimination of CD4 from the cell surface encouraged investigators to examine why HIV has to reduce the cell surface expression of its own receptor. By analogy with other retroviruses, it was first speculated that removal of CD4 from the cell surface would impede superinfection of cells, an eve...

Excessive proliferation and migration of vascular smooth muscle cells (SMCs) participate in atherosclerotic plaque growth. In this study, we investigated whether SMCs from vessels with different atherogenicity exhibit distinct growth and migratory potential and investigated the underlying mechanisms. In fat-fed rabbits, we found increased cell proliferation and atheroma formation in the aortic arch versus the femoral artery. When examined in culture, SMCs isolated from the aortic arch (ASMCs) displayed a greater capacity for inducible proliferation and migration than paired cultures of femoral artery SMCs. Two lines of evidence suggested that distinct regulation of the growth suppressor p27 Kip1 (p27) contributes to establishing these phenotypic dissimilarities. First, p27 expression was comparably lower in ASMCs, which exhibited a higher fraction of p27 phosphorylated on Thr-187 and ubiquitinated. Second, forced p27 overexpression in ASMCs impaired their proliferative and migratory potential. We found that platelet-derived growth factor-BB-dependent induction of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway was comparably higher in ASMCs. Importantly, pharmacological inhibition of MAPKs increased p27 expression and attenuated ASMC proliferation and migration. In contrast, forced MAPK activation diminished p27 expression and markedly augmented femoral artery SMC proliferation and migration. We propose that intrinsic differences in the regulation of MAPKs and p27 play an important role in creating variance in the proliferative and migratory capacity of vascular SMCs, which might in turn contribute to establishing regional variability in atherogenicity.

More than half of all global deaths in 2010 were related to non-communicable diseases, including obesity, cancers, diabetes, and cardiovascular illnesses. It has been suggested that the alarming increase in the incidence of cardiovascular disease is the epidemiologic result of a nutrition transition characterized by dietary patterns featuring an increase in the intake of total fat, cholesterol, sugars, and other refined carbohydrates, concomitant with low consumption of polyunsaturated fatty acids and fiber. Although traditional dietary approaches have proven successful as part of the treatment for obesity and cardiometabolic derangements within clinical trial scenarios, they lack effectiveness in the long term, mainly due to poor compliance. Research has thus turned its attention to nutraceutics, nutrients that have the ability to modulate physiological and pathophysiological molecular mechanisms, thus resulting in favorable health outcomes. Polyphenols have been considered as among the bioactive molecules as they are thought to yield beneficial effects by exerting antioxidant activity; however, there are other--and even more robust--metabolic pathways through which polyphenols enhance cardiovascular health, such as via promoting vasodilatory, anti-atherogenic, antithrombotic, and anti-inflammatory effects. No standard dose has yet been determined, as the effects greatly vary among polyphenols and food sources; thus, there is an imperative need to generate more evidence in order to support dietary recommendations aimed at the prevention and therapeutics of obesity and its associated cardiometabolic diseases.

We sought to determine the relative importance of aging and hypercholesterolemia on atherosclerosis. Although plasma cholesterol levels increased similarly in young and old rabbits fed an atherogenic diet for 2 months, aortic atherosclerotic lesions were more prominent in young animals. This ¢nd-ing was associated with an age-dependent reduction in the DNA-binding activity of the proin£ammatory nuclear factor U UB (NF-U UB) in aortic tissue. Atherosclerotic lesions consisted mostly of macrophages, which displayed a similar proliferative response in both age groups. Independently of the age, medial cell proliferation was low and increased as a function of intimal lesion size. Thus, higher atherogenicity in young rabbits exposed to extreme hypercholesterolemia compared to old counterparts is associated with higher activity of NF-U UB in the juvenile vessel wall without apparent age-dependent changes in arterial cell proliferation. ß 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.