# RelA Inhibits Embryonic Myogenesis by Coordinately Regulating a Novel Distal Enhancer of Myogenin

## TL;DR

Maternal obesity impairs muscle development in embryos by increasing RelA activity, which blocks a key muscle gene, but this effect can be reversed with metformin.

## Contribution

Identifies a novel distal enhancer of myogenin regulated by RelA and shows how maternal obesity disrupts embryonic myogenesis through this mechanism.

## Key findings

- Maternal obesity upregulates RelA in embryonic myogenic cells, impairing myotube formation.
- RelA binds to a 4 kb distal enhancer of Myog, inhibiting its expression and myogenesis.
- Metformin treatment suppresses RelA activity, restoring Myog expression and myogenic differentiation.

## Abstract

Skeletal muscle is crucial for lifelong metabolic health, with its development initiating during embryogenesis and guiding later growth. Single‐cell RNA sequencing of E13.5 mouse embryos suggests that maternal obesity impairs embryonic myogenesis, primarily during myotube formation, and is correlated with the downregulation of myogenin (Myog) expression. Spatial transcriptomic sequencing further confirms these findings. Conversely, maternal obesity induces the upregulation of RelA, a transcription factor and inflammatory signaling effector, in the myogenic cells of obese embryos. Additionally, single‐cell ATAC sequencing suggests that a cis‐regulatory region, located 4 kb proximal to the Myog promoter, exhibits coordinated expression with Myog and acts as an enhancer of Myog. In obese embryonic myogenic cells, RelA is recruited to this region, inhibiting Myog expression and myotube formation. Notably, in vitro RelA knockdown or inhibition rescues Myog expression and promotes myogenic differentiation. Similarly, metformin treatment of obese mothers restores embryonic Myog expression and myogenesis by suppressing RelA. Together, the multi‐omics analyses demonstrate that RelA targets a distal Myog enhancer to coordinately inhibit Myog expression and embryonic myogenesis.

Maternal obesity (MO) accounts for more than 40% of pregnancies in the United States, induces inflammation, and impairs embryonic myogenesis, known to program muscle dysfunction in offspring. Inflammation enhances the binding of RelA to a novel distal enhancer located 4 kb upstream of myogenin promoter to inhibit embryonic myogenesis, which is recovered by metformin treatment during early pregnancy.