Grhl3 Downregulation Facilitates ECM Adaptation for Fibroblast to iCM Commitment

Area of Science:

• Regenerative Medicine
• Cardiovascular Biology
• Molecular Biology

Background:

• Direct cardiac reprogramming is a promising strategy for heart regeneration, converting fibroblasts into induced cardiomyocytes (iCMs).
• Extracellular matrix (ECM) remodeling significantly impacts cardiac disease and repair, but its role and regulation during reprogramming are not fully understood.

Purpose of the Study:

• To investigate the dynamic changes and transcriptional regulation of ECM during iCM reprogramming.
• To identify critical ECM components and regulators that act as barriers to cardiac reprogramming.

Main Methods:

• Integrated transcriptomic, proteomic, and epigenetic analyses of ECM dynamics during iCM reprogramming.
• Loss-of-function screening to identify ECM components and regulators, including integrin alpha-8 (Itga8) and grainyhead-like protein 3 homolog (Grhl3).
• Mechanistic studies using RNA sequencing, mass spectrometry, and CUT&Tag to define Grhl3-dependent regulation; in vitro and in vivo functional assessments.

Main Results:

• Cardiac reprogramming induced significant ECM remodeling, affecting collagen, fibrillar proteins, and integrins.
• Itga8 was identified as an ECM component restricting iCM conversion via the TGF-β/SMAD pathway.
• Grhl3 was identified as a key regulator of ECM components, including Itga8. Grhl3 depletion enhanced iCM induction, fibroblast plasticity, and in vivo cardiac repair post-myocardial infarction.

Conclusions:

• ECM adaptation is a critical determinant of cardiac reprogramming efficiency and success.
• Grhl3 is a key regulator of ECM remodeling during cardiac reprogramming and represents a potential therapeutic target for myocardial repair.