HIV-1 Nef impairs key functional activities in human macrophages through CD36 downregulation.
Monocytes and macrophages utilize the class A and B scavenger receptors to recognize and perform phagocytosis of invading microbes before a pathogen-specific immune response is generated. HIV-1 Nef protein affects the innate immune system impairing oxidative burst response and phagocytic capacity of macrophages. Our data show that exogenous recombinant myristoylated Nef protein induces a marked CD36 downregulation in monocytes from Peripheral Blood Mononuclear Cells, in Monocyte-Derived Macrophages (MDMs) differentiated by cytokines and in MDMs contained in a mixed culture obtained expanding PBMCs under Human Erythroid Massive Amplification condition. Under the latter culture condition we identify three main populations after 6 days of expansion: lymphocytes (37.8 ± 14.7%), erythroblasts (46.7±6.1%) and MDMs (15.7 ± 7.5%). The Nef addition to the cell culture significantly downregulates CD36 expression in MDMs, but not in erythroid cells. Furthermore, CD36 inhibition is highly specific since it does not modify the expression levels of other MDM markers such as CD14, CD11c, CD86, CD68, CD206, Toll-like Receptor 2 and Toll-like Receptor 4. Similar results were obtained in MDMs infected with VSV-G pseudotyped HIV-1-expressing Nef. The reduced CD36 membrane expression is associated with decrease of correspondent CD36 mRNA transcript. Furthermore, Nef-induced CD36 downregulation is linked to both impaired scavenger activity with reduced capability to take up oxidized lipoproteins and to significant decreased phagocytosis of fluorescent beads and GFP-expressing Salmonella tiphymurium. In addition we observed that Nef induces TNF-α release in MDMs. Although these data suggest a possible involvement of TNF-α in mediating Nef activity, our results exclude a possible relationship between Nef-induced TNF-α release and Nef-mediated CD36 downregulation. The present work shows that HIV-1 Nef protein may have a role in the strategies elaborated by HIV-1 to alter pathogen disease outcomes, by modulating CD36 expression in macrophages, favoring the onset of opportunistic infections in HIV-1 infected people.
National AIDS Centre, Istituto Superiore di Sanità, Rome, Italy.
Eleonora
E
Olivetta
Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
Valentina
V
Tirelli
National AIDS Centre, Istituto Superiore di Sanità, Rome, Italy.
Chiara
C
Chiozzini
Department of Veterinary, Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
Beatrice
B
Scazzocchio
Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
Ignazio
I
Romano
National AIDS Centre, Istituto Superiore di Sanità, Rome, Italy; Department of Science, University Roma TRE, Rome, Italy.
Claudia
C
Arenaccio
Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy.
Massimo
M
Sanchez
D018955:CD36 Antigens / Q000378:metabolism*; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000276:immunology; D017931:DNA Primers / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects / Q000276:immunology*; D008264:Macrophages / Q000378:metabolism*; D010587:Phagocytosis / Q000187:drug effects; D060888:Real-Time Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D012486:Salmonella typhimurium / Q000378:metabolism; D018709:Statistics, Nonparametric; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000378:metabolism* / Q000494:pharmacology
D018955:CD36 Antigens; D017931:DNA Primers; D011994:Recombinant Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1; D049452:Green Fluorescent Proteins