22: When RNases Hide the Message: Naked exRNA, Immune Sensing, and Translation

Castellano M et al., Cell Genomics - This study shows that extracellular ribonucleases mask the bioactivity of naked extracellular RNA (exRNA). When RNases are inhibited or absent, naked exRNA is internalized, triggers endosomal and cytosolic RNA sensors, and can enable translation of delivered mRNAs. Key terms: extracellular RNA, ribonuclease, TLR13, gymnosis, mRNA translation.

Study Highlights:
Inhibition or absence of extracellular RNases reveals that naked exRNA is spontaneously internalized by diverse cell types and induces pro-inflammatory responses. Internalized exRNA activates endosomal Toll-like receptors (including mouse TLR13 for bacterial rRNA) and, after endosomal escape, cytosolic RIG-I–like receptors via MAVS. Stabilized naked mRNAs can be translated in recipient cells in an RNase-dependent manner. In vivo RNase inhibition amplifies systemic immune activation while RNase-poor compartments (e.g., peritoneal cavity) respond to naked exRNA without added inhibitor.

Conclusion:
Extracellular RNases are a key barrier that prevents immune sensing and functional uptake of naked exRNA; controlling RNase activity reveals that nonvesicular exRNAs can mediate intercellular signaling, activate endosomal and cytosolic RNA sensors, and serve as translatable templates in recipient cells.

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-05-16.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 7
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title
- article_journal
- license

Factual Items Audited:
- Naked exRNA is bioactive when extracellular RNases are inhibited, triggering pro-inflammatory responses via endosomal TLRs and cytosolic RLRs.
- TLR13 recognizes bacterial 23S ribosomal RNA Ec12 in endosomes; endocytosis is required for the response.
- Naked exRNA can escape endosomes to the cytosol and activate MAVS-dependent cytosolic sensors (RIG-I/MDA5 in human cells).
- Naked mRNA can be translated in recipient cells when RNases are inhibited (gymnotic uptake).
- In vivo, systemic RNases limit exRNA signaling; RI co-injection enhances systemic inflammatory activation; RNase-poor compartments (peritoneal cavity) can respond without RI.
- RNases act as a regulatory shield preventing systemic inflammation; dysregulation of RNase activity relates to autoimmune contexts like lupus.

QC result: Pass.