Galectin-9 Mediates HIV Transcription by Inducing TCR-Dependent ERK Signaling

Abstract

Endogenous plasma levels of the immunomodulatory carbohydrate-binding protein galectin-9 (Gal-9) are elevated during HIV infection and remain elevated after antiretroviral therapy (ART) suppression. We recently reported that Gal-9 regulates HIV transcription and potently reactivates latent HIV. However, the signaling mechanisms underlying Gal-9-mediated viral transcription remain unclear. Given that galectins are known to modulate T cell receptor (TCR)-signaling, we hypothesized that Gal-9 modulates HIV transcriptional activity, at least in part, through inducing TCR signaling pathways. Gal-9 induced T cell receptor ζ chain (CD3ζ) phosphorylation (11.2 to 32.1%; P = 0.008) in the J-Lat HIV latency model. Lck inhibition reduced Gal-9-mediated viral reactivation in the J-Lat HIV latency model (16.8–0.9%; P < 0.0001) and reduced both Gal-9-mediated CD4 + T cell activation (10.3 to 1.65% CD69 and CD25 co-expression; P = 0.0006), and IL-2/TNFα secretion ( P < 0.004) in primary CD4 + T cells from HIV-infected individuals on suppressive ART. Using phospho-kinase antibody arrays, we found that Gal-9 increased the phosphorylation of the TCR-downstream signaling molecules ERK1/2 (26.7-fold) and CREB (6.6-fold). ERK and CREB inhibitors significantly reduced Gal-9-mediated viral reactivation (16.8 to 2.6 or 12.6%, respectively; P < 0.0007). Given that the immunosuppressive rapamycin uncouples HIV latency reversal from cytokine-associated toxicity, we also investigated whether rapamycin could uncouple Gal-9-mediated latency reactivation from its concurrent pro-inflammatory cytokine production. Rapamycin reduced Gal-9-mediated secretion of IL-2 (4.4-fold, P = 0.001) and TNF (4-fold, P = 0.02) without impacting viral reactivation (16.8% compared to 16.1%; P = 0.2). In conclusion, Gal-9 modulates HIV transcription by activating the TCR-downstream ERK and CREB signaling pathways in an Lck-dependent manner. Our findings could have implications for understanding the role of endogenous galectin interactions in modulating TCR signaling and maintaining chronic immune activation during ART-suppressed HIV infection. In addition, uncoupling Gal-9-mediated viral reactivation from undesirable pro-inflammatory effects, using rapamycin, may increase the potential utility of recombinant Gal-9 within the reversal of HIV latency eradication framework.

Possible role of plasma Galectin-9 levels as a surrogate marker of viremia in HIV infected patients on antiretroviral therapy in resource-limited settings

“…Galectin-9 has been shown to potently reactivate latent HIV in CD4 + T cells ex vivo [12]. Enhanced HIV transcription by Galectin-9 has been shown through T cell receptor (TCR) based ERK signalling [22]. Since viremic patients in our study were virologically failing patients on ART, we did not have viral load values at a very high end of the viral load scale.…”

Associations Between Plasma Immunomodulatory and Inflammatory Mediators With VACS Index Scores Among Older HIV-Infected Adults on Antiretroviral Therapy

“…Furthermore, in the cerebrospinal fluid of people living with HIV higher Gal-9 levels were closely linked to increased viremia and immune activation as well as lower cognitive performance (68). Mechanistically, Gal-9 is hypothesized to potentially contribute to NK cell dysfunction and the non-specific activation of T cells in HIV infection (69,70). Whether elevated endogenous Gal-9 levels contribute or sustain the state of chronic inflammation and immune activation and contribute to the progression of comorbid conditions during suppressive ART warrants further investigation.…”

Elevated Levels of Galectin-9 but Not Osteopontin in HIV and Tuberculosis Infections Indicate Their Roles in Detecting MTB Infection in HIV Infected Individuals

“…Reduction in Gal-9 levels after initiation of antitubercular treatment needs to be investigated further to determine the monitoring potential of Gal-9 levels in HIV/TB co-infection as was demonstrated in acute infections such as dengue and malaria (Chagan-Yasutan et al, 2013;Dembele et al, 2016). While there are reports on Gal-9 suppressing HIV infectivity, other reports demonstrated Gal-9 (Elahi et al, 2012) to enhance HIV transcription through T-cell receptor (TCR)-based ERK signaling as well as to increase its infectivity through indirect pathway (Bi et al, 2011;Colomb et al, 2019). Elevated Gal-9 levels in chronic HIV infection have been shown to correlate with markers of HIV disease progression (Jost et al, 2013;Tandon et al, 2014).…”

“…While there are reports on Gal-9 suppressing HIV infectivity, other reports demonstrated Gal-9 ( Elahi et al, 2012 ) to enhance HIV transcription through T-cell receptor (TCR)-based ERK signaling as well as to increase its infectivity through indirect pathway ( Bi et al, 2011 ; Colomb et al, 2019 ). Elevated Gal-9 levels in chronic HIV infection have been shown to correlate with markers of HIV disease progression ( Jost et al, 2013 ; Tandon et al, 2014 ).…”