Hemoglobin inhibits fibroblast-to-cardiomyocyte reprogramming via TLR2/TLR4-dependent chromatin compaction

Area of Science:

• Cardiovascular Biology
• Regenerative Medicine
• Molecular Cardiology

Background:

• Fibroblast-to-cardiomyocyte reprogramming is crucial for cardiac repair after injury.
• Signals within the injured heart influence reprogramming efficacy, but their identity remains largely unknown.

Purpose of the Study:

• To identify inhibitory factors affecting fibroblast-to-cardiomyocyte reprogramming in cardiac tissue.
• To elucidate the mechanism by which hemoglobin (Hb) suppresses this reprogramming process.

Main Methods:

• Mass spectrometry to identify proteins in cardiac tissue extracts.
• In vitro assays to assess fibroblast-to-cardiomyocyte reprogramming.
• Inhibition of Toll-like receptors (TLR2 and TLR4).
• Assay for transposase-accessible chromatin using sequencing (ATAC-seq) to analyze gene regulation.

Main Results:

• Cardiac tissue extracts negatively impacted reprogramming; hemoglobin (Hb) was identified as the most abundant protein.
• Hb suppressed cardiomyocyte marker expression and formation, an effect reversed by inhibiting both TLR2 and TLR4.
• ATAC-seq revealed Hb-induced remodeling of transcription factor networks, suppressing cardiomyocyte-specific gene expression.

Conclusions:

• Hb acts as a negative regulator of fibroblast-to-cardiomyocyte reprogramming.
• Hb exerts its suppressive effects via TLR2 and TLR4, leading to altered gene regulatory networks.
• These findings have significant implications for developing strategies for cardiac regeneration.