Constitutive activation of PI3-kinase signaling pathway downregulates TLR4-mediated TNF-alpha release in alveolar macrophages from asymptomatic HIV+ persons in vitro

Tachado SD, Li X, Swan K, Patel N, Koziel H
Source: J Biol Chem
Publication Date: (2008)
Issue: 283(48): 33191-8
Research Area:
Immunotherapy / Hematology
Cells used in publication:
Species: human
Tissue Origin: blood
Macrophage, human
Species: human
Tissue Origin: blood
Nucleofector® I/II/2b
Alveolar macrophages (AM) represent critical effector cells of innate immunity to infectious challenge in the lungs, and recognize bacterial pathogens through pattern recognition receptors such as Toll-like receptors (TLRs). Our prior work showed reduced TLR4-mediated TNF-a release in HIV+ macrophages, attributed in part to constitutive induction of cellular phosphatase MKP-1. PI3K may also regulate TLR-mediated cytokine release, but whether HIV infection influences PI3K signaling pathway and alters TLR4-mediated macrophage response has not been investigated. In the current study, surface TLR4 expression were similar but TLR4 activation (lipid A, 10 microg/ml) resulted in lower TNF-a release by HIV+ human macrophages compared to healthy cells, consistent with prior investigations. Pharmacological inhibition of PI3K (LY294002) normalized TNF-a release in HIV+ macrophages and augments ERK1/2 MAP kinase phosphorylation in response to lipid A. Importantly, HIV+ macrophages demonstrated increased constitutive PIP3 formation, increased phosphorylation of downstream signaling molecules Akt and GSK-3ss at Ser9, and reduced PTEN protein expression. As a functional assessment of GSK-3ss phosphorylation, TLR4-mediated IL-10 release was significantly higher in HIV+ human macrophages compared to healthy cells. Incubation of human macrophages with exogenous HIV nef protein induced phosphorylation of Akt and GSK-3ss (whereas phosphorylation was reduced by PI3K inhibition), and promoted IL-10 release. Taken together, these data demonstrate increased constitutive activation of the PI3K signaling pathway in HIV+ macrophages, and support the concept that PI3K activation (by HIV proteins such as nef) may contribute to reduced TLR4-mediated TNF-a release in HIV+ human macrophages and impair host cell response to infectious challenge.