Apoptotic endothelial cells release small extracellular vesicles loaded with immunostimulatory viral-like RNAs

Abstract

Endothelial cells have multifaceted interactions with the immune system, both as initiators and targets of immune responses. In vivo , apoptotic endothelial cells release two types of extracellular vesicles upon caspase-3 activation: apoptotic bodies and exosome-like nanovesicles (ApoExos). Only ApoExos are immunogenic: their injection causes inflammation and autoimmunity in mice. Based on deep sequencing of total RNA, we report that apoptotic bodies and ApoExos are loaded with divergent RNA cargos that are not released by healthy endothelial cells. Apoptotic bodies, like endothelial cells, contain mainly ribosomal RNA whereas ApoExos essentially contain non-ribosomal non-coding RNAs. Endogenous retroelements, bearing viral-like features, represented half of total ApoExos RNA content. ApoExos also contained several copies of unedited Alu repeats and large amounts of non-coding RNAs with a demonstrated role in autoimmunity such as U1 RNA and Y RNA. Moreover, ApoExos RNAs had a unique nucleotide composition and secondary structure characterized by strong enrichment in U-rich motifs and unstably folded RNAs. Globally, ApoExos were therefore loaded with RNAs that can stimulate a variety of RIG-I-like receptors and endosomal TLRs. Hence, apoptotic endothelial cells selectively sort in ApoExos a diversified repertoire of immunostimulatory “self RNAs” that are tailor-made for initiation of innate immune responses and autoimmunity.

Apoptotic cell-derived exosomes: messages from dying cells

“…In addition, in glioblastoma multiforme (GBM), an aggressive brain cancer, it was recently reported that components of the spliceosomes contained in ApoExos promote tumor cell proliferation and confer therapeutic resistance to live tumor cells via remodeling of the RNA splicing patterns 67 . Interestingly, ApoExos produced from endothelial cells deliver noncoding RNAs, characterized by sequences rich in uridine and reminiscent of viral RNAs, which can stimulate RIG-I-like receptors and TLRs to induce inflammation 68 , while ApoExos from thymocytes suppresses immune responses by induction of TGFβ in macrophages 69 .…”

Analytical Value of Cell-Free DNA Based on Alu in Psychiatric Disorders

“…In recent years, it has been reported that Alu played a role also in the process of inflammation (51,52). The injection of ApoExos containing unedited Alu repeats resulted in inflammation in mice (26). Alu had an influence on the inflammatory response mechanisms of atherosclerosis and coronary artery disease (53).…”

“…It can be released from apoptotic cells. Several copies of unedited Alu repeats were found by Hardy et al, contained in exosome-like nanovesicles (ApoExos), which were released by apoptotic endothelial cells (26). Alu has been utilized as a biomarker in many kinds of diseases including cancer (27,28).…”

Exosomes in Sepsis

“…Exosomal exRNAs are recognized by PRRs, such as TLRs, NLRs, and RIG-I-like receptors (RLRs) of their interacting cells and initiate immune response (45). A recent study showed that exosomes released from apoptotic endothelial cells contained enormous amount of diversified viral-like RNAs, which have potential to activate PRRs (46). Exosomes are abundant in microRNAs (miRNAs), small non-coding RNAs which regulate gene expression (44,47).…”