UC Irvine

Lamin A/C are intermediate filament proteins that construct the nuclear lamina of a cell encoded by the LMNA gene. Lamin A/C has been implicated in processes such as chromatin localization and cell differentiation. Consequently, mutations in LMNA have detrimental effect in cell functions which results in diseases collectively termed as laminopathies. Some diseases that are caused by defective Lamin A/C include cardiac diseases, which are the focus of this project. Whole exome sequencing on dilated cardiomyopathy patients identified a novel splice site mutation in intron 1 of LMNA (LMNA c.357-2A>G), which is predicted to result in exon skipping and subsequently Lamin A/C haploinsufficiency. This project aims to elucidate the molecular mechanism contributing to the pathology of cardiac diseases. Approaches include developing a disease model by differentiating patient-specific iPSCs to cardiomyocytes to recapitulate the disease in-vitro. Using the cardiomyocytes generated, RNA and protein studies were conducted to elucidate on the molecular mechanism of the splice-site LMNA mutation. Our results showed that there was monoallelic expression of wild type LMNA allele in patient fibroblasts and cardiomyocytes. Whereas, Lamin A/C protein expression remained equal between patient and control fibroblasts, we found significant reduction in Lamin A/C protein level in patient cardiomyocytes underscoring the tissue-specificity of laminopathies. Further studies using single cell RNA-sequencing (scRNA-seq) followed by pathway analysis revealed that there was delayed activation of crucial cardiogenic genes due to the inhibition of the BMP signaling pathway, combined with the activation of PTEN signaling pathway that prevented beta-catenin nuclear accumulation leading to suppression of Wnt signaling pathway activity. Furthermore, we managed to link Lamin A/C haploinsufficiency to the activation of signaling pathways associated with apoptosis and accumulation of DNA damage. Taken together, our studies highlighted the utility of iPSC-based disease modeling to study molecular mechanisms of diseases and identified possible signaling pathways that affected cardiomyocyte differentiation and contributed to the pathology of Lamin-associated cardiac diseases.