Abstract P1107: Lem2 Is Essential For Cardiac Development By Maintaining Nuclear Integrity

Abstract

Background: integrity is essential for compartmentalisation of nucleus and cytoplasm. Importantly, mutations in -encoding genes are the second-highest cause of familial dilated cardiomyopathy. One such protein that causes cardiomyopathy in humans and affects mouse heart development is Lem2. However, its role in heart remains poorly understood. Methods: We generated mice in which Lem2 was specifically ablated either in embryonic cardiomyocytes (Lem2 cKO) or adult cardiomyocytes (Lem2 iCKO) and carried out detailed physiological, tissue and cellular analyses. High resolution episcopic microscopy was used for 3D reconstructions and detailed morphological analyses. RNA-sequencing and immunofluorescence identified altered pathways and cellular phenotypes, and cardiomyocytes were isolated to interrogate nuclear integrity in more detail. In addition, echocardiography provided physiological assessment of Lem2 iCKO adult mice. Results: We found that Lem2 was essential for cardiac development, and hearts from Lem2 cKO mice were morphologically and transcriptionally underdeveloped. Lem2 cKO hearts displayed high levels of DNA damage, nuclear rupture, and apoptosis. Crucially, we found that these defects were driven by muscle contraction as they were ameliorated by inhibiting myosin contraction and L-type calcium channels. Conversely, Lem2 ablation in adult cardiomyocytes did not lead to overt cardiac dysfunction up to 18 months of age. Conclusions: Our data suggest that Lem2 is critical for integrity at the nascent in fetal hearts, and protects the nucleus from the mechanical forces of muscle contraction. In contrast, the adult heart is not detectably affected by Lem2 loss, perhaps owing to a more established and increased adaptation to mechanical stress. Taken together, these data provide insights into mechanisms underlying cardiomyopathy in patients with mutations in Lem2 and cardio-laminopathies in general.