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Kidney is one of the organs, as haematopoietic tissue and central nervous system, representing a reservoir of HIV-1, where the virus can exert a direct pathogenic activity. HIV-associated nephropathy (HIVAN) is the prominent illness among the numerous renal injuries occurring in HIV-1 infection. It is characterized by heavy proteinuria and rapid progression to end stage renal disease. Histopathologically, HIVAN is a collapsing form of focal segmental glomerulosclerosis with podocyte hyperplasia and dedifferentiation, associated with severe tubulopathy which is characterized by tubular apoptosis, microcysts, and interstitial fibrosis. Several clinical and experimental data point to a direct role of HIV-1 in kidney damage. In renal biopsies of HIVAN cases viral transcripts have been found in glomerular and tubular epithelial cells. Transgenic mice expressing replication-defective HIV proviral constructs develop a renal disease similar to HIVAN both from the histopathological and clinical point of view. In vitro studies using cultures of human renal cells have shown that HIV-1 can induce in glomerular and tubular cells distinct pathogenic effects, which mimic the pathological features of HIVAN in vivo. A large body of evidence suggests that an abnormal response of podocytes to HIV-1 infection and/or HIV-1 proteins is the key event in HIVAN pathogenesis. Since the highly-active antiretroviral therapy has demonstrated scant beneficial effects on the development of HIVAN, the elucidation of the pathogenic mechanisms activated by HIV-1 in the renal cells might allow designing specific therapeutic strategies.

In the present study, we evaluated whether motility of Kaposi's sarcoma (KS) spindle cells induced by HIV-1 Tat protein is dependent on the synthesis of platelet-activating factor (PAF). The results obtained indicate that Tat induced a dose-dependent synthesis of PAF from KS cells at a concentration as low as 0.1 ng/ml. PAF production started rapidly after Tat stimulation, peaking at 30 minutes and declining thereafter. Tat-induced cell migration was also a rapid event starting at 30 minutes. The motility was abrogated by addition of a panel of chemically unrelated PAF receptor antagonists (WEB 2170, CV 3988, CV 6209, and BN 52021), suggesting that the synthesized PAF mediates the motogenic effect of Tat. This effect was also present on cells plated on a type-I collagen-, fibronectin-, or basement membrane extract-coated surface. Expression of PAF receptor-specific mRNA was detected in KS cells. In addition, examination of the cytoskeletal organization showed that Tat-mediated KS cell redistribution of actin filaments and shape change was also inhibited by a PAF receptor antagonist. Moreover, PAF receptor blockade prevented the up-regulation of beta1 integrin and the down-regulation of alphavbeta3 observed after stimulation of KS cells with Tat. In conclusion, the results of the present study indicate that Tat-induced PAF synthesis plays a critical role in triggering the events involved in motility of KS cells.

HIV-1 Tat protein has been shown to induce chemotaxis and recruitment of monocytes. In the present study, we evaluated whether HIV-1 Tat protein was able to induce the synthesis of platelet-activating factor (PAF), which is a potent mediator of cell motility, and whether the synthesis of PAF was instrumental in triggering Tat-induced monocyte chemotaxis. The results obtained indicate that Tat, but not gp120 and gp41, induced a time-dependent synthesis of PAF from monocytes at concentration as low as 0.1 ng/ml. As inferred by the inhibitory effect of anti-Flt-1 antibody and by the desensitization of monocytes following preincubation with vascular endothelial growth factor, the synthesis of PAF by monocytes stimulated with Tat was induced by activation of vascular endothelial growth factor receptor 1. Moreover, the Tat-induced chemotaxis of monocytes was abrogated both by WEB 2170 and by CV 3988, two chemically unrelated PAF receptor antagonists, suggesting that the synthesized PAF modulates the chemotactic response of monocytes to Tat. In conclusion, the results of the present study indicate that Tat-induced PAF synthesis plays a critical role in triggering the events involved in the migratory response of monocytes.

HIV-infected patients suffer several renal syndromes, which can progress rapidly from renal insufficiency to end-stage renal disease. Histologically, HIV-induced nephropathy is characterized by prominent tubulopathy with apoptosis of tubular cells. Clinical and experimental evidence suggests that renal injury may be directly related to virus infection. Although HIV-1 is a polytropic and not solely lymphotropic pathogen, the susceptibility of renal cells to HIV-1 remains to be determined. This paper demonstrates in vitro the permissiveness of proximal tubular epithelial cells (PTEC) to HIV-1 and describes the effects of PTEC infection to explain the pathogenesis of tubular damage in vivo. The results indicate that PTEC express HIV-specific receptor and coreceptors and sustain virus replication. We observed that HIV-1 infection causes the death of tubular cells by triggering an apoptotic pathway involving caspase activation. Fas upregulation but not Fas ligand expression was found in the infected PTEC. However, after HIV-1 infection, tubular cells became susceptible to apoptosis induced through Fas stimulation. Caspase inhibition prevented the death of the infected PTEC in spite of persistent viral replication. These findings may explain the prominent histopathology of HIV-associated nephropathy and demonstrate that the apoptosis of nonlymphoid cells can be directly induced by HIV-1.

In vitro experiments indicate that components of the host present in body fluids may prevent the attachment of human immunodeficiency virus type 1 (HIV-1) to target cells. Fibronectin (Fn), a dimeric 440-kDa extracellular matrix adhesion protein, is secreted by mesenchymal cells and assembled into insoluble matrices. Fn exerts important effects on cell growth and differentiation through a number of discrete functional domains. Several microorganisms are known to bind Fn. We show that, under physiological conditions, HIV-1 gp120 and gp160 are capable of binding plasma and cellular Fn as well as laminin and vitronectin. Experiments were set up to analyze in detail the binding of HIV gp120 and gp160 to Fn. The gp120 and gp160 specifically recognize the C-terminal heparin-binding domain of Fn (Fn-CTHBD) with a calculated KD of 2.8 x 10(-7) M for gp160. Binding of gp160 to Fn-CTHBD is a saturable and specific process that is blocked by antibodies to Fn-CTHBD and by heparin and is inhibited to a minor extent by heparan sulfate and dextran sulfate. These observations suggest that gp120/160 specifically recognize the III15 repeat within Fn-CTHBD. Intact Fn and Fn-CTHBD strongly inhibit the interaction of gp120/160 with soluble CD4 and, under low serum conditions, are capable of neutralizing the infectivity of HIV-1 for CD4-positive T cells. Thus, Fn that is present in plasma and mucinous secretions may well affect HIV infectivity and virus distribution in vivo.

Vascular endothelial cells (EC) play a key role in viral tropism in vivo. Since conflicting reports have been published on the capability of HIV to infect EC in vitro, we analyzed some factors potentially capable of influencing the susceptibility of human umbilical vein endothelial cells (HUVEC) to HIV-1. Both primary cultures and differentiated immortalized HUVEC lines were used. HUVEC were negative for the expression of CD4, but weakly CD26- and galactosylceramide-positive. Although binding of HIV to EC was substantial, the virus was apparently incapable of replicating in nonproliferating cultures. In resting cultures, the content of cell-associated HIV disappeared 4-6 days after infection without production of p24 and infectious progency. In contrast, infection of proliferating EC cultures led to the transient release of p24 and infectious virus (10(2.5)-10(3.5) SFU/ml) peaking 2-6 days postinfection. Antibody neutralization of cytokines that may be produced by EC (IL1, IL6, IL8, TNF, IFN-beta) failed to modify virus adsorption and replication, whereas treatment with IL1-beta plus TNF-alpha stimulated both virus binding and virus release. As seen by gag polymerase chain reaction (PCR), the viral genome persisted up to 15 days in untreated EC cultures, but over 20 days in cultures exposed to IL1-beta plus TNF-alpha. This study shows that: (a) CD4-negative HUVEC are capable of binding substantial amounts of HIV-1; (b) binding is enhanced by proinflammatory cytokines; (c) the establishment of productive infection is favored by cell proliferation; and (d) exposure to IL1-beta plus TNF-alpha enhances virus replication.

Objective and Design: To determine the susceptibility of mammary epithelial cells (MEC) to HIV-1 as breastfeeding is an established route of HIV transmission, although the origin of virus in breastmilk is unclear., Methods: Primary epithelial cell cultures were derived from the mammary glands of healthy donors; immortalized MEC lines were also used. HIV infection was followed by detection of infectious particle production, p24 antigen and viral sequences., Results: Seven out of 11 primary MEC cultures and two out of three MEC lines were productively infected by HIV-1. Virus replication significantly reduced cell proliferation, although cell viability was only slightly affected. Cytopathic changes were not observed. MEC cultures expressed low levels of surface CD4, galactosylceramide and CD26, but essentially no human leukocyte antigen (HLA)-DR. Infection of HIV-permissive MEC cells was associated with the upregulation of surface HLA-DR and CD26. In contrast, the expression of CD4, tissue-specific markers, adhesion molecules and growth-factor receptors was downregulated. To a lesser extent, similar effects were also observed in non-permissive cells. Hormones (triiodothyronine plus beta-estradiol and prolactin) enhanced HIV replication, possibly through the stimulation of cellular DNA synthesis., Conclusions: We concluded that HIV-1 replication in ductal/alveolar MEC may be, in part, responsible for the presence of HIV-1 in milk; that hormones may stimulate virus replication; and that infection reduces the growth of epithelial cells. Although in vitro HIV is produced by MEC to a lesser extent than lymphoid cells, MEC-derived HIV might have selective advantages for the infection of mucosal epithelial cells during breastfeeding.