In the adult heart, regeneration after myocardial infarction (MI) is extremely limited. Enhancing cardiomyocyte (CM) proliferation represents a promising approach for inducing regenerative repair in the damaged heart. Long noncoding RNAs (lncRNAs) represent a class of epigenetic regulatory molecules controlling genes expression and thereby crucial regulators of cell identity and behavior.

Identification and characterization of lncRNAs inducing proliferation in cardiomyocytes in order to promote heart regeneration following myocardial infarction.

Three hundred and fifty antisense oligonucleotide were selected to knockdown (KD) individually 350 heart-enriched LncRNAs in a high-throughput screening assay in vitro using neonatal CMs. Mitochondrial dynamics and respiration were evaluated via Seahorse XF Analyzers and SIM microscopy respectively. The effect of Clipper KD on CM proliferation and heart function in vivo was investigated in a mouse model of MI.

We identified Clipper, a nuclear CM-enriched enhancer-associated lncRNA, located in the Lipin1 locus. Clipper KD induced significant CM proliferation in vitro, associated with a reduction of Lipin1 expression, indicating that Clipper could work via regulating Lpin1. Lpin1 encodes a transcriptional regulator involved in mitochondrial biogenesis. Upon Clipper KD, mitochondrial dynamics and function were decreased. In particular, mitochondrial asymmetric fission was reduced. Asymmetric fission is a response to oxidative stress and mitochondrial turnover under stress conditions. ROS, a major determinant of CM cell cycle arrest, are therefore reduced following Clipper KD in CMs. In vivo, CM proliferation is also observed after Clipper KD following MI. However, function is not restored, likely because energy metabolism is simultaneously affected.

This study suggests the existence of coordinated regulation of CM mitochondrial function and proliferation, in part through the Clipper/Lipin1 axis.