<EM>CIRCHTT(2,3,4,5,6)</EM> REGULATES PROTEIN TRANSLATION, MODULATING HUNTINGTON`S DISEASE PHENOTYPES

Circular RNA (circRNA) molecules have critical functions during brain development and in brain related disorders. We recently identified and validated a circRNA, circHTT(2,3,4,5,6), stemming from the Huntington's disease (HD) gene locus, most abundant in the central nervous system. We uncovered its evolutionary conservation in diverse mammalian species, and a correlation between circHTT(2,3,4,5,6) levels and the length of the CAG-repeat tract in exon-1 of HTT in human and mouse HD model-systems. The mouse orthologue, circHtt(2,3,4,5,6), is expressed during embryogenesis, increases during nervous system development and it is aberrantly up-regulated in presence of the expanded CAG-tract. CircHtt(2,3,4,5,6) over-expression experiments in the HD-relevant STHdh striatal cells, revealed its ability to modulate CAG-expansion driven cellular defects in cell-to-substrate adhesion (Morandell et al., 2024). While an IRES-like motif was predicted in circHtt(2,3,4,5,6), it doesn’t appear to be directly translated in adult mouse brain tissue. Through ribosome co-sedimentation experiments, we detected a modest, but consistent fraction of circHtt(2,3,4,5,6) associated with the 40S-ribosomal subunit, suggesting a possible role in the regulation of protein translation. Here, through circHtt(2,3,4,5,6) knock-down followed by RIBO-lace analysis of actively translating ribosomes, and circRNA pull-down experiments, followed by LC-MS detection of protein interactors of circHtt(2,3,4,5,6), we further elucidate its molecular function in physiologic conditions and in HD.