Role of Hydrogen Sulfide Gas in Modulating HIV-1 Latency and Reactivation
Human Immunodeficiency Virus 1 (HIV-1) remains a global public health threat, claiming 690 thousand people’s lives in 2020 and causing 1.5 million new infections. The advent of combinatorial antiretroviral therapy (ART) have curbed the spread of the HIV-1 epidemic by limiting new infections rate. However, ART is not a curative therapy, and HIV-1 persists in latent reservoirs mainly comprising long-lived memory CD4+ T cells. Notably, low ART treatment coverage and cases of poor therapy adherence lead to replenishment of latent reservoirs and the emergence of drug-resistant variants. Thus, to eradicate HIV-1, it is important to understand how the virus establishes latency, maintains stable cellular reservoirs, and promotes rebound upon interruption of antiretroviral therapy (ART). Cellular redox status has been observed as a key determinant modulating HIV-1 latency and reactivation. HIV-1 patients display the hallmark of oxidative stress with reduced levels of major cellular antioxidants, glutathione (GSH), and thioredoxin (Trx) systems. The current approach to target latent HIV-1 includes a ‘shock and kill’ approach, which utilizes latency reversing agents (LRAs) to reactivate HIV-1 and kill infected cells by immune-based mechanisms [Chapter 1]. The LRAs belonging to histone deacetylase inhibitors class, when used in combination with GSH biosynthesis inhibitor, BSO, induce robust oxidative stress and heightened HIV-1 reactivation. In this direction, the use of antioxidant molecules, e.g., N-acetyl cysteine (NAC), has been shown to limit HIV-1 reactivation, but the molecular mechanism involved in NAC action remains understudied. Recently, NAC has been shown to exert its effect by inducing the biogenesis of a novel antioxidant gasotransmitter molecule, hydrogen sulfide (H2S). Previously considered as a toxic gas, but literature in the past two decades suggests the cytoprotective and antioxidant role of H2S in several patho-physiological conditions. In this study, we were interested in comprehensively characterizing the role of H2S gas in modulating HIV-1 latency and reactivation program. Here we observed that HIV-1 reactivation is associated with the downregulation of the H2S biogenesis enzyme, CTH, resulting in the depletion of endogenous H2S levels. Moreover, depleting endogenous H2S levels via knockdown of CTH expression in the cells with latent HIV-1 results in an imbalance of redox homeostasis, increased GSSG levels, enhances mitochondrial ROS (mito-ROS), dysfunctional mitochondria, and thereby resulting in robust HIV-1 reactivation [Chapter 2]. Moreover, chemical complementation of H2S deficiency using GYY4137, a slow- releasing H2S donor, inhibited distinct LRAs induced HIV-1 reactivation in monocytic, T- lymphocytic cell line model and primary CD4+ T cells derived from ART-treated HIV-patients [Chapter 3]. Next, using the NanoString based targeted gene expression analysis, we found that HIV-1 reactivation with phorbol ester, PMA, is associated with the upregulation of genes known to induce ROS production, inflammation, and transcription factors involved in HIV-1 reactivation, e.g., NF-kB and FOS with concomitant downregulation of antioxidant machinery and viral suppressive factor, YY1. GYY4137 treatment reversed the PMA mediated effects and led to downregulation of genes involved in ROS production, inflammation and, concomitantly, enhanced the expression of NRF2 dependent antioxidant and antiviral genes [Chapter 4]. Furthermore, GYY4137 inhibited the activity of proviral factor NF-kB and enhanced the occupancy of an epigenetic repressor, YY1, on HIV-1 LTR. These mechanistic insights suggest that H2S inhibits HIV-1 reactivation by maintaining cellular redox status, limiting the activation of transcription factors required for active viral transcription, and inducing epigenetic suppression of viral LTR.