Mechanical memory stored through epigenetic remodeling reduces cell therapeutic potential

Area of Science:

• Biomedical Engineering
• Cell Biology
• Regenerative Medicine

Background:

• Current cartilage regeneration relies on 2D cell expansion, but the limits of mechanical priming and its effect on cell fate are unknown.
• Understanding cellular mechanical memory is crucial for designing effective biomaterials and medical therapies.

Purpose of the Study:

• To identify the threshold for mechanical priming that induces irreversible mechanical memory in chondrocytes.
• To elucidate the mechanisms by which physical environments influence cellular therapeutic potential.

Main Methods:

• Primary cartilage cells (chondrocytes) were expanded in 2D culture for 8 and 16 population doublings.
• Cells were transferred to 3D hydrogels to assess recovery of tissue-identifying gene expression.
• Chromatin architecture changes, specifically H3K9 trimethylation (H3K9me3), were analyzed.
• Epigenetic modifiers were manipulated to assess their impact on chromatin and cell phenotype.

Main Results:

• Chondrocytes expanded for 16 doublings failed to recover tissue-identifying gene expression in 3D culture, unlike those expanded for 8 doublings.
• Phenotypic changes correlated with alterations in chromatin architecture, specifically H3K9me3.
• Increasing H3K9me3 levels partially restored chromatin architecture and chondrogenic gene expression.

Conclusions:

• A threshold of 8 population doublings exists for reversible mechanical memory in chondrocytes.
• Chromatin architecture, regulated by H3K9me3, is a key factor in maintaining the chondrocyte phenotype.
• Epigenetic modifiers offer potential therapeutic targets to disrupt mechanical memory in cell-based regeneration.