MiR-21-5p Protects Embryonic Growth and Heart Function During Developmental Hypoxia by Dampening HIF Responses and...

Fetal hypoxia is a common complication of pregnancy and increases the cardiovascular risk in offspring, contributing to a significant burden on life-long health. Preventative strategies against its adverse effects have focused on targeting oxidative stress, but not epigenetic mechanisms. Since miRNA-21-5p downregulation contributes to fetal growth restriction (FGR) and cardiovascular impairment, we tested the hypothesis that miR-21 upregulation during developmental hypoxia is protective. The hypothesis was tested adopting an integrative approach, combining gene expression and transcript variant usage, profiling of neonatal rat cardiomyocytes (NRC) exposed to hypoxia and miR-21-5p mimic, and in vivo assessment of the effects of miR-21-5p on growth and cardiac function in hypoxic chicken embryos. In NRC, hypoxia resulted in 385 differentially expressed genes (DEG) relative to normoxia (FDR < 0.05; DEG; 142 down- and 243 up-regulated). In vitro miR-21-5p improved cell survival, completely dampened hypoxia-responsive genes, modified transcript isoform usage of key cardiac transcripts (i.e., Sfpq and Lgr4), attenuated apoptotic signaling, and shifted gene networks toward improved Ca²⁺ handling, β-adrenergic and PI3K-related pathways. In vivo miR-21-5p administration during incubation prevented asymmetric FGR, protected systolic and diastolic function, and normalized cardiac sympathetic dominance in hypoxic chicken embryos. These data suggest that miR-21-5p exerts post-transcriptional control, linking hypoxia sensing to effectors of cardiomyocyte survival and function, as well as protecting against FGR and cardiac dysfunction in development during chronic hypoxia. This work supports the significant translational potential of miRNA-21 not only as a biomarker, but also as a therapeutic target in high-risk pregnancy.