Contact-Induced Mitochondrial Polarization Supports HIV-1 Virological Synapse Formation

Abstract

Rapid HIV-1 spread between CD4 T lymphocytes occurs at retrovirus-induced immune cell contacts called virological synapses (VS). VS are associated with striking T cell polarization and localized virus budding at the site of contact that facilitates cell-cell spread. In addition to this, spatial clustering of organelles, including mitochondria, to the contact zone has been previously shown. However, whether cell-cell contact specifically induces dynamic T cell remodeling during VS formation and what regulates this process remain unclear. Here, we report that contact between an HIV-1-infected T cell and an uninfected target T cell specifically triggers polarization of mitochondria concomitant with recruitment of the major HIV-1 structural protein Gag to the site of cell-cell contact. Using fixed and live-cell imaging, we show that mitochondrial and Gag polarization in HIV-1-infected T cells occurs within minutes of contact with target T cells, requires the formation of stable cell-cell contacts, and is an active, calcium-dependent process. We also find that perturbation of mitochondrial polarization impairs cell-cell spread of HIV-1 at the VS. Taken together, these data suggest that HIV-1-infected T cells are able to sense and respond to contact with susceptible target cells and undergo dynamic cytoplasmic remodeling to create a synaptic environment that supports efficient HIV-1 VS formation between CD4 T lymphocytes.IMPORTANCE HIV-1 remains one of the major global health challenges of modern times. The capacity of HIV-1 to cause disease depends on the virus's ability to spread between immune cells, most notably CD4 T lymphocytes. Cell-cell transmission is the most efficient way of HIV-1 spread and occurs at the virological synapse (VS). The VS forms at the site of contact between an infected cell and an uninfected cell and is characterized by polarized assembly and budding of virions and clustering of cellular organelles, including mitochondria. Here, we show that cell-cell contact induces rapid recruitment of mitochondria to the contact site and that this supports efficient VS formation and consequently cell-cell spread. Additionally, we observed that cell-cell contact induces a mitochondrion-dependent increase in intracellular calcium, indicative of cellular signaling. Taken together, our data suggest that VS formation is a regulated process and thus a potential target to block HIV-1 cell-cell spread.

HIV Cell-to-Cell Spread Results in Earlier Onset of Viral Gene Expression by Multiple Infections per Cell

“…For example, it has been reported that the infected donor cell rapidly polarizes to the site of contact with the target cell [20] and that the subsequent transmission to the target cell occurs quickly [4, 18, 59, 60], though viral membrane fusion has been reported to be slower in cell-to-cell spread relative to cell-free infection [16]. Hence, a faster onset of HIV gene expression in cell-to-cell spread may be strictly mechanistic, due to more rapid entry of the virus.…”

Positive-sense RNA viruses reveal the complexity and dynamics of the cellular and viral epitranscriptomes during infection

“…The partial overlap between the arsenite-treated and virus-infected cells is not particularly surprising considering that arsenite is a potent inducer of oxidative stress resulting in mitochondrial damage (74,75), and that viral infections alter mitochondrial structure and function. For example, DENV and ZIKV have been shown to dampen the innate immune response by altering the structure of the mitochondria during infection (76), whereas HCV infection induces oxidative stress and mitophagy (77)(78)(79)(80)(81)(82) and HIV may re-localize and damage mitochondria (83,84). Therefore, the incomplete overlap may reflect a common response resulting from mitochondrial damage, as well as separate cellular response pathways that are uniquely activated by oxidative stress or viral infection.…”

Viruses exploit the tissue physiology of the host to spread in vivo

“…In the case of MLV, virus budding is polarized to areas on the plasma membrane where the clustering of Env at the cell-cell interface initiates the recruitment of Gag [12,33]. In contrast, HIV assembly is directed towards sites of cell-cell contact by polarization of the cytoskeleton and the secretory machinery [34,35], as well as spatial clustering of organelles such as mitochondria [36]. A structural analysis of the virological synapse between HIV-infected and non-infected T cells or astrocytes reveals a complex membrane organization with cell-type specific differences in the cell contact architecture and the distribution of sites for virus budding and release [37,38].…”