title: HIV impairs TNF-alpha release in response to Toll-like receptor 4 stimulation in human macrophages in vitro.
abstract: The molecular mechanisms for increased risk of bacterial pneumonia in HIV+ persons remain incompletely understood. Recognizing the critical role of Toll-like receptor (TLR) signaling in host defense, this study showed that human U937 macrophage stimulation by the TLR4-specific ligand, lipid A (biologically active component of bacterial LPS), promoted TNF-alpha release through extracellular regulated kinase (ERK)1/2 mitogen-activated protein (MAP) kinase phosphorylation. In contrast, HIV+ U1 macrophages had significantly reduced TNF-alpha release (despite preserved TLR4 expression) and reduced ERK1/2 phosphorylation, whereas TNF-alpha release was intact via a TLR4-independent pathway. In HIV+ U1 cells, reduced ERK1/2 phosphorylation was not due to reduced upstream MEK1/2 activation, but was associated with a reciprocal induction of MAP kinase phosphatase-1 (MKP-1). HIV nef protein was sufficient to reduce TNF-alpha release and induce MKP-1 in healthy macrophages. Pharmacologic inhibition of endogenous cellular phosphatases increased ERK1/2 phosphorylation and partially restored TLR4-mediated TNF-alpha release in HIV+ macrophages. Furthermore, targeted gene silencing of MKP-1 partially restored lipid A-mediated TNF-alpha release in HIV+ U1 cells. Similar results were observed using clinically relevant human alveolar macrophages, comparing healthy to asymptomatic HIV+ persons at clinical risk for bacterial pneumonia. Thus, reduced TLR4-mediated TNF-alpha release through altered ERK1/2 regulation by HIV may impair an effective innate immune response to bacterial challenge. Inhibition of cellular phosphatases may serve as a potential therapeutic target in the management of bacterial pneumonia in HIV+ persons.
authors.affiliation: Department of Pulmonary, Critical Care and Sleep Medicine, Kirstein Hall, Room E/KSB-23, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215, USA.
authors.forename: Souvenir D
authors.initials: SD
authors.lastname: Tachado
authors.forename: Jianmin
authors.initials: J
authors.lastname: Zhang
authors.forename: Jinping
authors.initials: J
authors.lastname: Zhu
authors.forename: Naimish
authors.initials: N
authors.lastname: Patel
authors.forename: Henry
authors.initials: H
authors.lastname: Koziel
mesh_terms: D016022:Case-Control Studies; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015693:Gene Products, nef / Q000502:physiology; D020868:Gene Silencing; D006678:HIV / Q000502:physiology*; D015658:HIV Infections; D006679:HIV Seropositivity; D006801:Humans; D017874:Immediate-Early Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D066298:In Vitro Techniques; D008050:Lipid A / Q000494:pharmacology; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D020298:U937 Cells; D054311:nef Gene Products, Human Immunodeficiency Virus; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D015693:Gene Products, nef; D017874:Immediate-Early Proteins; D008050:Lipid A; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D054311:nef Gene Products, Human Immunodeficiency Virus; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1; D017027:Protein Tyrosine Phosphatases