🧬 PubMed RNA Editing Daily Digest

The initial development of adenine base editors (ABEs), which facilitate A•T to G•C base pair changes in the genome, used directed evolution to install 14 mutations into the wild-type deaminase TadA, producing the first-of-its-kind editor ABE7.10. Here we study the installed mutations' impacts on TadA fitness using comprehensive reversion analysis and apply our results to engineer more efficient, precise editors. By measuring activity in both human and Escherichia coli host systems, we categorize mutations as critical, dispensable or host dependent. We show that up to five mutations can be reverted back to wild type, generating minimally evolved ABEs (ME-ABEs). ME-ABEs show narrow editing windows (similar to that of ABE7.10) and enhanced on-target editing (matching activities of the high-activity editor variants ABE8e and ABE8.20 in most sequence contexts) and exhibit low levels of guide-RNA-dependent and guide-RNA-independent off-target activity. ME-ABEs efficiently target six sites of clinical interest that had previously proved challenging to edit with ABE7.10, ABE8e or ABE8.20.

Telomere maintenance has been portrayed primarily as a problem of DNA-protein architecture and chromatin control, yet a complementary layer has been revealed at the level of RNA chemistry. In this Review, RNA modifications and their writer-reader-eraser and RNA-editing systems are integrated into a framework for chromosome-end homeostasis. Epitranscriptomic regulation of the telomerase ribonucleoprotein is examined, and assembly, activity, and recruitment are shown to be reshaped by chemical marks on TERC, specialized RNA capping, and processing pathways. Telomeric transcripts, particularly TERRA, are discussed as modified substrates whose stability, trafficking, and propensity for telomeric RNA: DNA hybrid formation can be tuned by RNA marks and their readers. Downstream consequences for replication stress, DNA damage signaling, and recombination-driven alternative lengthening of telomeres are summarized, together with emerging examples in which modification of telomere-factor mRNAs has been linked to rewiring of maintenance networks. Across these themes, links to telomeropathies, aging-associated inflammation, environmental stressors, and cancer are collated to connect mechanism to phenotype. Experimental bottlenecks and opportunities-site-resolved mapping, locus-targeted editing, and pharmacologic modulation of RNA-modifying enzymes-are outlined as routes toward causal models and therapeutic utilization.

Adenosine-to-inosine RNA editing by ADAR1 prevents aberrant innate immunity activation by modifying endogenous double-stranded RNA. Mice carrying a left-handed double-stranded RNA (Z-RNA) binding-deficient mutation develop Aicardi-Goutières syndrome (AGS)-like encephalopathy, characterized by ventricular enlargement, gliosis, calcification, and white matter degeneration with a type I interferon (IFN) signature. However, the mechanisms underlying encephalopathy development remain unknown. Here, we show that pathology was most severe in periventricular regions where IFN-stimulated gene (ISG) expression was elevated and ependymal cells were lost, accompanied by higher IFN-α levels in cerebrospinal fluid than in sera. Blocking type I IFN signaling fully reversed these abnormalities, which was not achieved by deleting downstream PKR or ZBP1. Microglial elimination partially alleviated the encephalopathy without suppressing ISGs. In contrast, neuron- or astrocyte-specific ADAR1 dysfunction evoked robust ISG expression and recapitulated AGS-like encephalopathy, with astrocytic dysfunction causing particularly severe effects. These findings identify aberrant multicellular IFN signaling as the central driver of AGS-like encephalopathy.

Dilated cardiomyopathy (DCM) is a leading cause of heart failure (HF), yet molecular signatures that are detectable in blood and mechanistically anchored in myocardial pathology remain limited. Adenosine-to-inosine (A-to-I) RNA editing is an important post-transcriptional regulator in the heart, but its biomarker potential in human DCM and its reflection in the circulation are not well defined. We performed comprehensive RNA editome profiling of human myocardium from DCM patients and non-failing donors, and integrated these results with peripheral blood RNA editing profiles from HF patients and controls, using a SPRINT-based pipeline with stringent in-house post-postprocessing and quality filtering. Global editing distributions and site-level differential editing were assessed, and shared heart-blood candidates were evaluated for directionality and functional enrichment. Cardiac RNA editing was dominated by ADAR-mediated A-to-I events and was significantly increased in DCM, with prominent enrichment in Alu elements and a higher number of unique editing sites compared with controls. Site-level analysis identified a predominantly hyper-edited DCM signature, mapping to genes and pathways linked to cardiomyopathy and cellular stress, including hypoxia and apoptosis. Cross-tissue comparison revealed 107 shared differentially edited sites between DCM heart and HF blood, with subsets showing concordant directionality. Shared targets were enriched for innate immune and type I interferon signaling, RIG-I pathway regulation, hypoxia-related responses, and apoptosis. DCM is associated with global myocardial A-to-I hyper-editing and a robust, multi-locus editing program. Importantly, a subset of these disease-associated editing events is detectable in peripheral blood from heart failure patients, supporting the feasibility of HF-associated circulating RNA editing signatures that reflect myocardial pathology.