# Microgravity-induced transcriptional reprogramming in embryonic chicken limb bud-derived chondrogenic cultures

## TL;DR

This study shows how simulated microgravity affects gene activity in cartilage cells from chicken embryos, revealing changes in key genes and pathways related to cartilage development.

## Contribution

The study identifies specific gene expression changes and signaling pathway disruptions in chondrogenic cultures under simulated microgravity, including consistent upregulation of ADRB1.

## Key findings

- Continuous microgravity exposure caused significant differential expression of 648 genes, including suppression of SOX9 and COL2A1 and upregulation of MMP13 and ADAMTS.
- Key pathways affected include TGF-β/BMP balance, Wnt/β-catenin activation, and cytoskeletal remodeling.
- ADRB1 was consistently upregulated across all microgravity exposure time points.

## Abstract

Extended exposure to microgravity, such as experienced during spaceflight, significantly alters the mechanical environment of skeletal tissues, impacting cartilage development and function. Mechanical unloading disrupts the balance of cellular signaling and extracellular matrix synthesis in cartilage precursor cells, but the molecular consequences and temporal dynamics of these alterations remain incompletely understood.

We employed simulated microgravity via a random positioning machine (RPM) to investigate stage-specific transcriptomic and phenotypic responses in chondrogenic micromass cultures derived from embryonic chicken (Gallus gallus) limb bud cells. RNA sequencing, bioinformatic pathway analysis, and protein interaction network construction were performed on cultures exposed to microgravity for early (days 0–3), late (days 3–6), and continuous (days 0–6) periods.

Continuous microgravity exposure resulted in robust differential expression of 648 genes (adjusted p-value <0.05, |log2 fold change| > 1), including suppression of canonical chondrogenic markers (SOX9, COL2A1) and upregulation of catabolic enzymes (MMP13, ADAMTS family). The affected key signaling pathways included disrupted TGF-β/BMP balance, Wnt/β-catenin activation, and cytoskeletal remodeling. Early and late exposures showed consistent gene expression trends but fewer statistically significant changes. Notably, adrenergic beta receptor 1 (ADRB1) was consistently upregulated across all time points.

These findings demonstrate that simulated microgravity rapidly induces reversible molecular and cellular adaptations related to cartilage homeostasis and mechanotransduction in this chondrogenic model system. The RPM platform offers a powerful tool to dissect chondrogenesis, cartilage biology, and lineage plasticity under mechanical unloading, providing insights with broad relevance to skeletal tissue mechanobiology.