HUNTINGTON'S DISEASE-ASSOCIATED SMALL RNAS TRIGGER DIFFERENTIAL IMMUNE ACTIVATION

The small RNA (sRNA) landscape is altered in Huntington’s disease (HD), with multiple studies reporting the dysregulation of specific sRNA classes, including microRNAs (miRNAs) and tRNA fragments (tRFs), in patients’ brains. tRFs are generated by the cleavage of mature cytoplasmic tRNAs, and are known to accumulate in cells under pathological conditions, where they can not only engage canonical stress-response pathways, but also activate RNA-sensing machinery, thereby triggering downstream inflammatory signaling pathways. Through deep sRNA-sequencing, our group identified tRFs as the most abundant sRNA species dysregulated in human HD post-mortem putamen samples, and subsequent qRT-PCR analysis of selected candidate sequences validated their upregulation in HD vs control individuals, in independent, age- and sex-matched samples. Interestingly, this increase was not observed in the homologous brain region of the R6/1 murine model of HD. To further investigate this, we evaluated the potential immunogenicity of a subset of upregulated tRFs and miRNAs in human THP-1 cells differentiated into macrophages, a commonly used model with well-characterized RNA-sensing machinery. Exposure to the selected sRNA species elicited distinct inflammatory profiles that were both dose-dependent and sequence-specific. Immunogenicity was assessed by measuring the release of pro-inflammatory cytokines to the culture supernatant, as well as by evaluating the ability of the sequences to induce the expression of RNA-sensing molecules. Together, the stress-induced increase in tRNA fragmentation and the immunogenic properties of these sRNA species may contribute to the neuroinflammatory process associated with HD.