MiR-19b-3p Regulates MAPK1 Expression in Embryonic Fibroblasts from the Great Tit (Parus Major) Under Hypoxic Conditions

Background/Aims: Genomic adaptations to high altitudes have been well studied in the last several years; however, the roles of microRNAs (miRNAs), which are essential modulators of a variety of genes and key cellular processes, have rarely been explored. Here, we explored the interactions between miRNAs and their target genes as an adaptation to high altitude in an avian species, the great tit ( Parus major ), which is widely distributed across the Eurasian continent at altitudes between 4500 m and sea level. Because the MAPK signaling pathway plays a crucial role in the hypoxia response in the great tit, we chose MAPK1 as a target candidate gene. Methods: We established a great tit embryonic fibroblast line and subsequently studied the relationship between miRNA-19b-3p and MAPK1 in normoxia and hypoxia groups. Meanwhile, the great tit embryonic fibroblasts (GEFs) were treated or transfected with miR-19b-3p mimics, inhibitors, or si-MAPK1, and their proliferation was subsequently assessed using the MTT assay. The expression of the miRNAs and MAPK1 was measured by real-time PCR and Western blotting. Results: We identified 14 miRNAs in the cardiac tissues of great tits that are related to hypoxia adaptation. MAPK1 binds only to miR-19b-3p of the 14 miRNAs predicted by both TargetScan and miRanda software. Specifically, we validated the computational prediction of miR-19b-3p binding to the 3’UTR of MAPK1 using a luciferase reporter assay. Our results show that miR-19b-3p promotes GEFs proliferation and up-regulates MAPK1 expression. Moreover, miR-19b-3p mimics and MAPK1 knockdown induce GEFs apoptosis and regulate the cell cycle under hypoxic conditions. Conclusions: Our study is the first to describe an important miRNA-mediated regulatory mechanism of high altitude adaptation in a non-model wild songbird and highlights the importance of studies on miRNA-mediated mechanisms of hypoxic adaptations in other animals.