ABSTRACT: Purpose: Post-traumatic epilepsy (PTE) is an epilepsy that develops after traumatic brain injury (TBI), and it comprises 10-20% of structural epilepsies and 5% of all epilepsies. The lack of prognostic biomarkers for PTE hinders the development of anti-epileptogenic treatments. In this preclinical multicenter study, plasma samples collected from a rat model of PTE were analyzed by small RNA sequencing to reveal the post-TBI expression profile of circulating microRNAs and to identify potential miRNA biomarkers for PTE development. Methods: The animal experiments were conducted at 3 different study sites: University of Eastern Finland (Finland), Monash University (Australia), and University of California, Los Angeles (USA). Severe TBI was induced in adult male Sprague-Dawley rats by the lateral fluid-percussion injury (LFPI) method. Rats that developed PTE were identified by video-EEG monitoring during the 7th post-injury month (TBI rats with epilepsy, TBIE; TBI rats without epilepsy, TBIN). Small RNA sequencing was conducted with plasma samples collected 48 hours after TBI or sham operation (craniotomy). Following the primary quantification, DESeq2 (v. 1.42.0) was used to identify differentially expressed miRNAs between the experiment groups. Results were further validated in a larger sample cohort by droplet digital PCR (ddPCR). Results: Small RNA sequencing detected a total of 754 miRNAs that were expressed in at least one sample. DESeq2 detected 23 differentially expressed (DE) miRNAs between the TBI and sham groups, 12 between the TBIE and sham groups, and 5 between the TBIN and sham groups. In contrast, no DE miRNAs were detected between the TBIE and TBIN groups. From the list of 23 DE miRNAs between the TBI and sham groups, 3 upregulated miRNAs (rno-miR-183-5p, rno-miR-323-3p, and miR-434-3p) were selected for further ddPCR validation. The list of miRNAs for validation was further complemented by 4 miRNAs (rno-miR-9a-3p, rno-miR-124-3p, rno-miR-132-3p, and rno-miR-212-3p), which were not differentially expressed in the DESeq2 analysis, but which we have previously detected to be acutely upregulated in TBI rat plasma. The validation was conducted with samples from the entire EpiBioS4Rx cohort [26 baseline samples, 45 sham, 164 TBI (32 TBIE, 132 TBIN)]. DdPCR analysis revealed that all 7 investigated miRNAs were upregulated in the TBI rats compared with the sham controls. No differences were detected between the rats with (TBIE) or without epilepsy (TBIN). In contrast, TBIE rats that had seizure clusters (severe PTE) had lower levels of plasma miR-212-3p compared with other TBI rats. Furthermore, elastic net regularized logistic regression (glmnet) analysis identified miR-212-3p and miR-132-3p as the optimal set to differentiate TBIE rats with seizure clusters from other TBI rats. Conclusions: The profile of circulating plasma microRNAs differed between TBI rats and sham controls. MiR-212-3p alone or in combination with miR-132-3p showed potential as prognostic biomarkers for development of severe PTE.