Molecular Basis of Intron Retention in mRNA from Osteoarthritis Synoviocytes.

Intron retention (IR) is one of the cellular mechanisms to perform alternative splicing and thus control gene expression in several mammalian cellular pathways. IR in mRNA was observed in some primary synoviocyte samples from osteoarthritis (OA) patients, likely due to inter-patient variability. The aim of the present manuscript was to explore the IR molecular mechanism as a consequence of nutraceutical treatment of synoviocytes and the molecular basis of individual response. To evaluate the gene expression modulation of molecules involved in mRNA splicing, an RNA-seq analysis was performed, and the transcription modulation of six differentially expressed genes was validated by RT-PCR. Moreover, through a silencing experiment, the relationship between IR and the six modulated genes was explored. Finally, two of them, the RNA-binding proteins CELF1 and PTBP3, whose mRNA levels were elevated in samples exhibiting IR, were analyzed in detail. CELF1 and PTBP3 were overexpressed in synoviocytes lacking IR, and we found that CELF1 was responsible for IR, whereas PTBP3 did not seem to be involved. In conclusion, in our experimental model, the role of CELF1 protein in IR was explored, opening new scenarios for understanding the molecular mechanisms underlying the IR phenomenon present in several kinds of diseases.