Exosomes from HIV-1-infected Cells Stimulate Production of Pro-inflammatory Cytokines through Trans-activating Response (TAR) RNA

Abstract

HIV-1 infection results in a chronic illness because longterm highly active antiretroviral therapy can lower viral titers to an undetectable level. However, discontinuation of therapy rapidly increases virus burden. Moreover, patients under highly active antiretroviral therapy frequently develop various metabolic disorders, neurocognitive abnormalities, and cardiovascular diseases. We have previously shown that exosomes containing trans-activating response (TAR) element RNA enhance susceptibility of undifferentiated naive cells to HIV-1 infection. This study indicates that exosomes from HIV-1-infected primary cells are highly abundant with TAR RNA as detected by RT-real time PCR. Interestingly, up to a million copies of TAR RNA/l were also detected in the serum from HIV-1-infected humanized mice suggesting that TAR RNA may be stable in vivo. Incubation of exosomes from HIV-1-infected cells with primary macrophages resulted in a dramatic increase of proinflammatory cytokines, IL-6 and TNF-␤, indicating that exosomes containing TAR RNA could play a direct role in control of cytokine gene expression. The intact TAR molecule was able to bind to PKR and TLR3 effectively, whereas the 5 and 3 stems (TAR microRNAs) bound best to TLR7 and -8 and none to PKR. Binding of TAR to PKR did not result in its phosphorylation, and therefore, TAR may be a dominant negative decoy molecule in cells. The TLR binding through either TAR RNA or TAR microRNA potentially can activate the NF-B pathway and regulate cytokine expression. Collectively, these results imply that exosomes containing TAR RNA could directly affect the proinflammatory cytokine gene expression and may explain a possible mechanism of inflammation observed in HIV-1-infected patients under cART.

Immunological Profiles in HIV Positive Patients with or without Opportunistic Infections and the Influence of Highly Active Antiretroviral Therapy: A Systematic Review and Update

“…Toll like receptor binding via TAR RNA or TAR microRNA has the potential to activate nuclear factor-kappa beta (NF-κB) pathway thereby regulating cytokine expression. This explains a possible inflammation mechanism that is normally observed in patients infected with HIV who are under combination ART [93].…”

“…Incubation of macrophages with exosomes retrieved from HIV-1 infected cells has been shown to result in dramatic elevations of pro-inflammatory cytokines tumor necrosis factor-beta (TNF-β) and Interleukin (IL)-6 hence indicating that exosomes with TAR RNA can play a role in controlling cytokine gene expression [93]. Toll like receptor binding via TAR RNA or TAR microRNA has the potential to activate nuclear factor-kappa beta (NF-κB) pathway thereby regulating cytokine expression.…”

Potential of Radiation-Induced Cellular Stress for Reactivation of Latent HIV-1 and Killing of Infected Cells

“…We presume that cells may be blocked at the early, mid, or late G1 phase with the help of viral noncoding RNAs, such as free TAR RNA. 44 We recently have shown that TAR is present in cART-treated cells where it activates the TLR3 pathway and deregulates protein kinase R innate immune response, which could presumably keep cells away from G0 and be maintained at early G1 phase. Alternatively, if cells do pass into the G2 phase, there is high translation of viral proteins such as Vpr, which not only blocks cells at G2/M but also further activates DNA damage response.…”

The Role of HTLV-1 in Alteration of Immune Regulation Through Regulatory T Cell Dysfunction and Exosomal Manipulation

“…HIV, which has been noted to take advantage of several steps in exosome biogenesis, has been shown to incorporate transactivating response (TAR) RNA into exosomes [88,89]. The uptake of exosomal TAR in recipient cells can downregulate apoptosis and is postulated to have a role in supporting HIV infection.…”

“…Importantly, TAR RNA was still able to be detected in exosomes isolated from the serum of HIV-positive patients on highly active antiretroviral therapy, indicating that even with antiretroviral therapy, short transcripts remain present in these exosomes [90]. Indeed, the same group later went on to find that exosomal TAR RNA could stimulate proinflammatory cytokines in recipient cells through activation of the nuclear factor kappa b pathway [89]. In a separate study, the HIV Nef protein was found in released exosomes [91].…”