Exosomes contribute to the transmission of anti-HIV activity from TLR3-activated brain microvascular endothelial cells to macrophages

Abstract

Human brain microvascular endothelial cells (HBMECs), the major cell type in the blood-brain barrier (BBB), play a key role in maintaining brain homeostasis. However, their role in the BBB innate immunity against HIV invasion of the central nervous system (CNS) remains to be determined. Our early work showed that TLR3 signaling of HBMECs could produce the antiviral factors that inhibit HIV replication in macrophages. The present study examined whether exosomes from TLR3-activated HBMECs mediate the intercellular transfer of antiviral factors to macrophages. Primary human macrophages could take up exosomes from TLR3-activated HBMECs. HBMECs-derived exosomes contained multiple antiviral factors, including several key IFN-stimulated genes (ISGs; ISG15, ISG56, and Mx2) at mRNA and protein levels. The depletion of exosomes from TLR3-activated HBMECs culture supernatant diminished HBMECs-mediated anti-HIV activity in macrophages. In conclusion, we demonstrate that exosomes shed by HBMECs are able to transport the antiviral molecules to macrophages. This finding suggests the possibility that HIV nonpermissive BBB cells (HBMECs) can help to restore the antiviral state in HIV-infected macrophages, which may be a defense mechanism against HIV neuroinvasion.

ISG15 in antiviral immunity and beyond

“…ISG15 inhibited the activity of NEDD4 and blocked the ubiquitylation of VP40 and the interaction between NEDD4 and ubiquitin E2 conjugating enzymes, preventing ubiquitin from being transferred to NEDD4 (refS 39,69 ). Interestingly, a recent study found that ITCH, another E3 ubiquitin ligase, also interacts with VP40 to Although it does not possess a leader signal sequence to direct its secretion, ISG15 has been found to be released through microparticles 146 , exosomes 35 and neutrophilic granules 5 ; from secretory lysosomes 36 ; and via apoptosis 36 . It has been described as influencing the functions of several different types of cells.…”

“…T cells: ISG15 was found to induce the secretion of IFNγ 147 . Macrophages: ISG15-containing microparticles and exosomes have been found to stimulate macrophages to secrete pro-inflammatory cytokines 146 and mediate anti-HIV activity 35 , respectively. It remains to be determined whether it is a stand-alone effect of ISG15 or an effect synergistic with those of other molecules in the secretory vesicles.…”

“…Extracellular ISG15 has been proposed to function as a cytokine with several immunomodulatory activities, including the induction of natural killer (NK) cell proliferation 32 , the stimulation of interferon-γ (IFNγ) production 5 and the induction of dendritic cell maturation 33 , and to function as a chemotactic factor for neutrophils 34 . Its mechanism of release is unclear as ISG15 does not contain a leader signal; however, recent studies have shown that it could be released via non-conventional secretion, including in exosomes 35 , through the release of neutrophil granules from secretory lysosomes or via apoptosis 36 . Recently, lymphocyte function-associated antigen 1 (LFA1) was identified as a cell surface receptor for extracellular ISG15.…”

Strategies to Target ISG15 and USP18 Toward Therapeutic Applications

“…Although ISG15 does not have a leader signal sequence to direct its secretion, it has been shown that certain cell types are capable of releasing ISG15 to the extracellular space. Such cell types are epithelial-derived cell lines, fibroblasts, monocytes, neutrophils and lymphocytes (Knight and Cordova, 1991;Bogunovic et al, 2012;Sun et al, 2016). Extracellular ISG15 has been detected in the media of cells as well as in the serum of patients treated with IFN-α/β (D'Cunha et al, 1996).…”

Expression of CCL5 is induced by polyinosinic : polycytidylic acid in cultured hCMEC/D3 human brain microvascular endothelial cells

“…Toll‐like receptor 3 (TLR3) is a pattern‐recognition receptor for double‐stranded RNA, and recognition of viral double‐stranded RNA by TLR3 triggers the antiviral innate immune reactions. It has been reported that TLR3 and its polymorphisms play a crucial role in various viral infections of the nervous system, and that TLR3 is expressed in brain microvascular endothelial cells . However, details of TLR3 signaling in brain microvascular endothelial cells have not been well characterized.…”