ABSTRACT
Noonan syndrome patients harboring causative variants in LZTR1 are particularly at risk to develop severe and early-onset hypertrophic cardiomyopathy. In this study, we investigate the mechanistic consequences of a homozygous variant LZTR1L580P by using patient-specific and CRISPR-Cas9-corrected induced pluripotent stem cell (iPSC) cardiomyocytes. Molecular, cellular, and functional phenotyping in combination with in silico prediction identify an LZTR1L580P-specific disease mechanism provoking cardiac hypertrophy. The variant is predicted to alter the binding affinity of the dimerization domains facilitating the formation of linear LZTR1 polymers. LZTR1 complex dysfunction results in the accumulation of RAS GTPases, thereby provoking global pathological changes of the proteomic landscape ultimately leading to cellular hypertrophy. Furthermore, our data show that cardiomyocyte-specific MRAS degradation is mediated by LZTR1 via non-proteasomal pathways, whereas RIT1 degradation is mediated by both LZTR1-dependent and LZTR1-independent pathways. Uni- or biallelic genetic correction of the LZTR1L580P missense variant rescues the molecular and cellular disease phenotype, providing proof of concept for CRISPR-based therapies.
Subject(s)
Induced Pluripotent Stem Cells , Myocytes, Cardiac , Noonan Syndrome , ras Proteins , Humans , Noonan Syndrome/genetics , Noonan Syndrome/pathology , Noonan Syndrome/metabolism , Myocytes, Cardiac/metabolism , Myocytes, Cardiac/pathology , Induced Pluripotent Stem Cells/metabolism , Induced Pluripotent Stem Cells/pathology , ras Proteins/metabolism , ras Proteins/genetics , Transcription Factors/metabolism , Transcription Factors/genetics , Mutation/genetics , Cardiomyopathy, Hypertrophic/genetics , Cardiomyopathy, Hypertrophic/pathology , Cardiomyopathy, Hypertrophic/metabolism , Polymerization , CRISPR-Cas Systems/genetics , Proteolysis , Mutation, Missense , Protein Multimerization , Genes, Recessive , PhenotypeABSTRACT
Noonan syndrome (NS), the most common among RASopathies, is caused by germline variants in genes encoding components of the RAS-MAPK pathway. Distinct variants, including the recurrent Ser257Leu substitution in RAF1, are associated with severe hypertrophic cardiomyopathy (HCM). Here, we investigated the elusive mechanistic link between NS-associated RAF1S257L and HCM using three-dimensional cardiac bodies and bioartificial cardiac tissues generated from patient-derived induced pluripotent stem cells (iPSCs) harboring the pathogenic RAF1 c.770 C > T missense change. We characterize the molecular, structural, and functional consequences of aberrant RAF1-associated signaling on the cardiac models. Ultrastructural assessment of the sarcomere revealed a shortening of the I-bands along the Z disc area in both iPSC-derived RAF1S257L cardiomyocytes and myocardial tissue biopsies. The aforementioned changes correlated with the isoform shift of titin from a longer (N2BA) to a shorter isoform (N2B) that also affected the active force generation and contractile tensions. The genotype-phenotype correlation was confirmed using cardiomyocyte progeny of an isogenic gene-corrected RAF1S257L-iPSC line and was mainly reversed by MEK inhibition. Collectively, our findings uncovered a direct link between a RASopathy gene variant and the abnormal sarcomere structure resulting in a cardiac dysfunction that remarkably recapitulates the human disease.
Subject(s)
Cardiomyopathy, Hypertrophic , Noonan Syndrome , Proto-Oncogene Proteins c-raf , Humans , Cardiomyopathy, Hypertrophic/genetics , Cardiomyopathy, Hypertrophic/metabolism , Cardiomyopathy, Hypertrophic/pathology , Germ-Line Mutation , Myocytes, Cardiac/metabolism , Noonan Syndrome/genetics , Noonan Syndrome/complications , Noonan Syndrome/metabolism , Signal Transduction , Proto-Oncogene Proteins c-raf/geneticsABSTRACT
Patients harboring causative gene variants in RAS GTPase MRAS develop Noonan syndrome and early-onset hypertrophic cardiomyopathy. Here, we describe the generation of a human iPSC line harboring the Noonan syndrome-associated MRAS p.G23V variant by using CRISPR/Cas9 technology. The established MRASG23V iPSC line allows to study MRAS-specific pathomechanisms and to test novel therapeutic strategies in various disease-relevant cell types and tissues.
Subject(s)
Cardiomyopathy, Hypertrophic , Induced Pluripotent Stem Cells , Noonan Syndrome , Humans , Noonan Syndrome/genetics , Noonan Syndrome/metabolism , Induced Pluripotent Stem Cells/metabolism , Cardiomyopathy, Hypertrophic/genetics , ras Proteins/genetics , ras Proteins/metabolism , MutationABSTRACT
Activating KRAS codon 12 gene variants are known to cause severe RAS-MAPK and PI3K-AKT signaling pathway hyperactivity and are frequently involved in the development of various carcinomas. Here, we describe the generation of a human iPSC line harboring the common oncogenic KRAS p.G12V variant by using CRISPR/Cas9 technology. The established KRASG12V iPSC line allows the study of oncogenic KRAS-induced signaling dysregulation and its impact on cell physiology in various iPSC-derived cell types and tissues. Furthermore, it might serve as a powerful platform for drug and toxicity screenings to identify new chemotherapeutic drugs.
Subject(s)
Induced Pluripotent Stem Cells , Humans , Induced Pluripotent Stem Cells/metabolism , Proto-Oncogene Proteins p21(ras)/genetics , Proto-Oncogene Proteins p21(ras)/metabolism , Phosphatidylinositol 3-Kinases/genetics , Phosphatidylinositol 3-Kinases/metabolism , Signal Transduction , Mutation/geneticsABSTRACT
BACKGROUND: Brugada syndrome (BrS) is causing sudden cardiac death (SCD) mainly at young age. Studying the underlying mechanisms associated with BrS type I electrocardiogram (ECG) changes in the presence of fever and roles of autophagy for BrS remains lacking. OBJECTIVES: We sought to study the pathogenic role of an SCN5A gene variant for BrS with fever-induced type 1 ECG phenotype. In addition, we studied the role of inflammation and autophagy in the pathomechanism of BrS. METHODS: Human-induced pluripotent stem cell (hiPSC) lines from a BrS patient harboring a pathogenic variant (c.3148G>A/p. Ala1050Thr) in SCN5A and two healthy donors (non-BrS) and a CRISPR/Cas9 site-corrected cell line (BrS-corr) were differentiated into cardiomyocytes (hiPSC-CMs) for the study. RESULTS: Reductions of Nav 1.5 expression, peak sodium channel current (INa ) and upstroke velocity (Vmax ) of action potentials with an increase in arrhythmic events were detected in BrS compared to non-BrS and BrS-corr cells. Increasing the cell culture temperature from 37 to 40°C (fever-like state) exacerbated the phenotypic changes in BrS cells. The fever-effects were enhanced by protein kinase A (PKA) inhibitor but reversed by PKA activator. Lipopolysaccharides (LPS) but not increased temperature up to 40°C enhanced the autophagy level in BrS-hiPSC-CMs by increasing reactive oxidative species and inhibiting PI3K/AKT signalling, and hence exacerbated the phenotypic changes. LPS enhanced high temperature-related effect on peak INa shown in BrS hiPSC-CMs. Effects of LPS and high temperature were not detected in non-BrS cells. CONCLUSIONS: The study demonstrated that the SCN5A variant (c.3148G>A/p.Ala1050Thr) caused loss-of-function of sodium channels and increased the channel sensitivity to high temperature and LPS challenge in hiPSC-CMs from a BrS cell line with this variant but not in two non-BrS hiPSC-CM lines. The results suggest that LPS may exacerbate BrS phenotype via enhancing autophagy, whereas fever may exacerbate BrS phenotype via inhibiting PKA-signalling in BrS cardiomyocytes with but probably not limited to this variant.