Dysregulated microRNAs in blood correlate with central nervous system neuropathology of prion disease

The role of microRNAs (miRNAs) in neurodegenerative diseases has gained significant attention due to their involvement in gene regulation and potential as biomarkers. In prion diseases, including scrapie, miRNAs may modulate pathogenesis and disease progression. This study investigated circulating miRNA profiles in blood of sheep naturally affected by scrapie at preclinical and clinical stages using small RNA sequencing and RT-qPCR validation. While only one novel miRNA was dysregulated in preclinical blood samples, 66 previously identified miRNAs were significantly dysregulated in clinical sheep compared to healthy ones. These miRNAs were associated with pathways commonly altered in neurodegenerative diseases, such as autophagy, ubiquitin-mediated proteolysis, and endoplasmic reticulum protein processing. Notably, miR-1271-5p, let-7f-5p, miR-186-5p, and miR-425-5p showed consistent upregulation in the central nervous system of clinical animals, replicating the results observed in blood, with an increasing trend already in the preclinical stage and a strong correlation with neuropathological prion features. Additionally, predicted target genes such as UBQLN2, PGK1, KRAS, and CLTC were inversely expressed relative to these miRNAs, supporting their regulatory roles. These findings highlight the relevance of circulating miRNAs in prion neuropathology and support further research into the specific functional roles of these miRNAs and their predictive capacity for disease progression. Small RNA sequencing profiling of blood from naturally scrapie-affected sheep in the preclinical stage (n=5) and clinical stage (n=10) of the disease, compared to healthy control sheep (n=10), using the Illumina HiSeq 2500 platform.