Abstract 449: Post-transcriptionally Modified TRNA-derived Small RNA On HDL Antagonize Atherosclerosis Inflammation

Atherosclerotic cardiovascular disease (ASCVD) is a complex disease of uncontrolled hypercholesterolemia and inflammation. High-density lipoproteins (HDL) have been shown to suppress atherogenesis through multiple processes; however, many of HDL’s beneficial properties are lost during ASCVD. While the underlying reasons for the switch are unknown, changes to the composition and chemical properties of HDL cargo are likely a primary contributing factor. We have previously reported that HDL transfer microRNAs to recipient cells where they regulate gene expression. Based on our small RNA (sRNA) sequencing data, HDL also transports multiple classes of host and non-host sRNAs, including sRNAs-derived from parent tRNAs (tDRs). Recent studies indicate that extracellular sRNAs are post-transcriptionally modified and provide an additional layer of gene regulation. The current barrier to studying HDL-sRNA modifications is that modified sRNAs are often not captured by conventional sRNA sequencing approaches. To overcome this barrier, we have performed AlkB-facilitated RNA Methylation sequencing which removes common modifications on sRNAs prior to sequencing that normally would interfere with reverse transcription. Preliminary results support that HDL-tDRs are indeed heavily modified and conventional sequencing approaches greatly underestimate extracellular HDL-sRNA abundances. Previous work has established that modified sRNA antagonizes inflammation, primarily through inhibition of endosomal RNA-sensing toll-like receptors (i.e., TLR8) within immune cells. On the contrary, other studies have demonstrated that unmodified extracellular sRNAs can serve as TLR8 agonists. Due to the observations that a) HDL is highly-enriched in tDRs, b) HDL-tDRs are post-transcriptionally modified, c) modified sRNAs inhibit TLR signaling and inflammation, we hypothesize that modifications to HDL-tDRs confer antagonism towards immune cell activation and atherosclerosis inflammation.