Fibroblast State Reversal By MBNL1-Dependent Transcriptome Modification Regulates Cardiac Repair

Abstract

Dynamic fibroblast state transitions are responsible for the hearts fibrotic response to injury, raising the possibility that tactical control of these transitions could alter maladaptive fibrotic outcomes. Transcriptome maturation by the RNA binding protein Muscleblind Like 1 (MBNL1) has emerged as a potential driver of differentiated cell states. Here genetic lineage tracing of myofibroblasts in the injured heart demonstrated that gains in MBNL1 function corresponded to profibrotic fibroblast states. Similarly, in mice cardiac fibroblast specific MBNL1 overexpression induced a transcriptional myofibroblast profile in healthy cardiac fibroblasts that prevented the fibroproliferative phase of cardiac wound healing. By contrast loss of MBNL1 reverted cardiac fibroblasts to a pro-proliferative epicardial progenitor state that limited cardiac fibrosis following myocardial infarction. This progenitor state transition was associated with an MBNL1-dependent destabilization of the mesenchymal transition gene, Sox9. These findings suggest that MBNL1 regulation of the fibroblast transcriptome drives state transitions underlying cardiac fibrosis and repair.