Small Extracellular Vesicle Enrichment of a Retrotransposon-Derived Double-Stranded RNA: A Means to Avoid Autoinflammation?

Repetitive element transcript accumulation is associated with inflammaging in humans

Chronic, low-grade inflammation increases with aging, contributing to functional declines and diseases that reduce healthspan. Growing evidence suggests that transcripts from repetitive elements (RE) in the genome contribute to this "inflammaging" by stimulating innate immune activation, but evidence of RE-associated inflammation with aging in humans is limited. Here, we present transcriptomic and clinical data showing that RE transcript levels are positively related to gene expression of innate immune sensors, and to serum interleukin 6 (a marker of systemic inflammation), in a large group of middle-aged and older adults. We also: (1) use transcriptomics and whole-genome bisulfite (methylation) sequencing to show that many RE may be hypomethylated with aging, and that aerobic exercise, a healthspan-extending intervention, reduces RE transcript levels and increases RE methylation in older adults; and (2) extend our findings in a secondary dataset demonstrating age-related changes in RE chromatin accessibility. Collectively, our data support the idea that age-related RE transcript accumulation may play a role in inflammaging in humans, and that RE dysregulation with aging may be due in part to upstream epigenetic changes.

Small extracellular vesicles-shuttled miR-23a-3p from mesenchymal stem cells alleviate renal fibrosis and inflammation by inhibiting KLF3/STAT3 axis in diabetic kidney disease

Human umbilical cord mesenchymal stem cells-derived small extracellular vesicles (MSC-sEV) provide a pragmatic solution as a cell-free therapy for patients with diabetic kidney disease (DKD). However, the underlying protective mechanisms of MSC-sEV remain largely unknown in DKD. Invivo and in vitro analyses demonstrated that MSC-sEV attenuated renal fibrosis and inflammation of DKD. The underlying mechanism of the MSC-sEV-induced therapeutic effect was explored by high-throughput sequencing, which identified the unique enrichment of a set of miRNAs in MSC-sEV compared with human skin fibroblasts-sEV (HSF-sEV). Vitro experiments demonstrated that the protective potential was primarily attributed to miR-23a-3p, one of the most abundant miRNAs in MSC-sEV. Further, overexpression or knockdown analyses revealed that miR-23a-3p, and its target Krüppel-like factor 3 (KLF3) suppressed the STAT3 signaling pathway in high glucose (HG) induced HK-2 cells were essential for the renal-protective property of MSC-sEV. Moreover, we found that miR-23a-3p was packaged into MSC-sEV by RNA Binding Motif Protein X-Linked (RBMX) and transmitted to HG-induced HK-2 cells. Finally, inhibiting miR-23a-3p could mitigate the protective effects of MSC-sEV in db/db mice. These findings suggest that a systemic administration of sEV derived from MSC, have the capacity to incorporate into kidney where they can exert renal-protective potential against HG-induced injury through delivery of miR-23a-3p.

Unpacking extracellular vesicles: RNA cargo loading and function

Extracellular vesicles (EVs) are a heterogeneous group of membrane-enclosed structures produced by prokaryotic and eukaryotic cells. EVs carry a range of biological cargoes, including RNA, protein, and lipids, which may have both metabolic significance and signalling potential. EV release has been suggested to play a critical role in maintaining intracellular homeostasis by eliminating unnecessary biological material from EV producing cells, and as a delivery system to enable cellular communication between both neighbouring and distant cells without physical contact. In this review, we give an overview of what is known about the relative enrichment of the different types of RNA that have been associated with EVs in the most recent research efforts. We then examine the selective and non-selective incorporation of these different RNA biotypes into EVs, the molecular systems of RNA sorting into EVs that have been elucidated so far, and the role of this process in EV-producing cells. Finally, we also discuss the model systems providing evidence for EV-mediated delivery of RNA to recipient cells, and the implications of this evidence for the relevance of this RNA delivery process in both physiological and pathological scenarios.

Origins and Function of VL30 lncRNA Packaging in Small Extracellular Vesicles: Implications for Cellular Physiology and Pathology

Long non-coding RNAs (lncRNAs) have emerged during the post-genomic era as significant epigenetic regulators. Viral-like 30 elements (VL30s) are a family of mouse retrotransposons that are transcribed into functional lncRNAs. Recent data suggest that VL30 RNAs are efficiently packaged in small extracellular vesicles (SEVs) through an SEV enrichment sequence. We analysed VL30 elements for the presence of the distinct 26 nt SEV enrichment motif and found that SEV enrichment is an inherent hallmark of the VL30 family, contained in 36 full-length elements, with a widespread chromosomal distribution. Among them, 25 elements represent active, present-day integrations and contain an abundance of regulatory sequences. Phylogenetic analysis revealed a recent spread of SEV-VL30s from 4.4 million years ago till today. Importantly, 39 elements contain an SFPQ-binding motif, associated with the transcriptional induction of oncogenes. Most SEV-VL30s reside in transcriptionally active regions, as characterised by their distribution adjacent to candidate cis-regulatory elements (cCREs). Network analysis of SEV-VL30-associated genes suggests a distinct transcriptional footprint associated with embryonal abnormalities and neoplasia. Given the established role of VL30s in oncogenesis, we conclude that their potential to spread through SEVs represents a novel mechanism for non-coding RNA biology with numerous implications for cellular homeostasis and disease.