Comparative study of gene regulatory and structural mechanisms in Lamin-related cardiomyopathy - PROJECT SUMMARY LMNA-related dilated cardiomyopathy (LMNA-DCM) is one of the most severe forms of adult-onset DCM and results from heterozygous loss-of-function mutations in Lamin A/C (LMNA), a key nuclear lamina component. Currently, no therapeutic interventions exist for LMNA-DCM, primarily due to an incomplete understanding of its molecular pathogenesis. This proposed study aims to directly compare two long-standing prevailing hypotheses regarding LMNA-DCM pathogenesis, the gene regulatory hypothesis and the structural hypothesis. The gene regulatory hypothesis proposes that Lamin A/C reduction causes relaxation of lamina-associated heterochromatin domains (LADs) causing pathogenic gene de-repression, while the structural hypothesis posits that Lamin A/C reduction weakens the nuclear envelope causing pathogenic nuclear envelope (NE) rupture. No studies have compared these mechanisms directly or examined their potential interrelation, a gap we aim to fill to advance mechanistic understanding of this disease. In preliminary studies, we unveiled that Lamin A/C’s requirement in cardiomyocytes arises during the postnatal fetal-to-adult heart maturation. This maturation period involves the repression of fetal gene programs and strengthening of the nuclear envelope to withstand expanding sarcomeres, both processes potentially relying on Lamin A/C’s gene regulatory and structural roles. Thus, our central hypothesis is that Lamin A/C is essential for maintaining LAD-associated gene repression and/or preventing NE rupture during postnatal cardiomyocyte maturation. To test this hypothesis, we will use two innovative mouse models: one with a cardiomyocyte-specific Lmna knockout (LmnaCKO) and another with a pathogenic LMNA-DCM frameshift mutation (LmnaFS), both of which expose Lamin A/C’s requirement during this maturation stage. Aim 1 will determine whether LmnaCKO and LmnaFS mice develop LAD disruption and associated de-repression of LAD-associated genes during postnatal cardiomyocyte maturation. Aim 2 will determine whether cardiomyocytes of LmnaCKO and LmnaFS mice exhibit NE rupture, independently or concurrently with LAD disruption, during this maturation phase. Aim 3 will assess the contributions of the LAD disruption and NE ruptures to the development of DCM. We will use LINC complex disruption to rescue LMNA- DCM in our mouse models, and examine whether LAD disruption or NE ruptures are primarily responsible for the disease. The anticipated impact of this study is to provide decisive evidence supporting one of these prevailing hypotheses, thereby accelerating the development of therapeutic strategies for LMNA-DCM.
