TRIM28 secures skeletal stem cell fate during skeletogenesis by silencing neural gene expression and repressing...

Area of Science:

• Developmental biology
• Stem cell biology
• Epigenetics

Background:

• Long bone development relies on skeletal progenitor/stem cells (SSCs) differentiating via endochondral ossification.
• This process is regulated by intrinsic and microenvironment factors.
• The role of transcriptional corepressors like TRIM28 in SSC fate is not fully understood.

Purpose of the Study:

• To investigate the function of TRIM28 in mesoderm-derived skeletal progenitor/stem cells (SSCs).
• To elucidate the molecular mechanisms by which TRIM28 influences SSC osteochondrogenic potential and lineage commitment.

Main Methods:

• CRISPR-Cas9 mediated knockout of TRIM28 in mesoderm-derived cells.
• Analysis of SSC proliferation, differentiation, and lineage potential.
• Chromatin immunoprecipitation sequencing (ChIP-seq) for H3K9 trimethylation and DNA methylation.
• RNA sequencing to assess gene expression changes.
• Western blotting and immunofluorescence to detect protein expression and localization.

Main Results:

• TRIM28 loss in SSCs led to an expanded progenitor pool but reduced osteochondrogenic potential.
• SSCs lacking TRIM28 acquired properties resembling ectoderm-derived neural crest cells (NCCs).
• TRIM28 deficiency resulted in decreased H3K9 trimethylation and DNA methylation, upregulating neural gene expression.
• GREM1 was hyperexpressed in TRIM28-deficient SSCs, promoting self-renewal and neurogenic potential via AKT/mTORC1 signaling.

Conclusions:

• TRIM28-mediated chromatin silencing is crucial for maintaining the SSC lineage trajectory.
• TRIM28 acts as a barrier preventing SSCs from transitioning to an ectodermal fate.
• TRIM28 regulates both intrinsic and microenvironment cues to ensure proper skeletal development.