Biallelic LZTR1 Mutations Activate RAS- MAPK Signaling and Cause Hypertrophic Cardiomyopathy in iPSC-Derived Cardiomyocytes of a Novel Type of Noonan Syndrome

by Ulrich Hanses
Doctoral thesis
Date of Examination:2023-02-28
Date of issue:2023-02-06
Advisor:Prof. Dr. Gerd Hasenfuß
Referee:Prof. Dr. Gerd Hasenfuß
Referee:Prof. Dr. Bernd Wollnik
Referee:Prof. Dr. Ralf Dressel
Persistent Address: http://dx.doi.org/10.53846/goediss-9682

 

 

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Abstract

English

Noonan syndrome is a multisystemic disorder with variable expressivity, characterized by typical craniofacial features, physical and mental retardation with cardiovascular abnormalities. Noonan syndrome is the most common mono-genetic congenital heart disease and manifests as pulmonary valve stenosis, atrial and/or ventricular septum defect, and hypertrophic cardiomyopathy. In most cases, Noonan syndrome is caused by autosomal dominant germline mutations leading to hyperactivity of the RAS-MAPK pathway. Despite the epidemiological relevance, the understanding of variable expressivity, pathophysiological changes, and mechanisms, especially of congenital heart diseases, and effective causal therapies remains limited. This study focuses on two siblings with a particularly pronounced form of hypertrophic cardiomyopathy caused by a recently discovered autosomal recessive mutations in leucine zipper like transcription regulator 1. Obtained skin biopsies from both siblings were reprogrammed to establish a Noonan syndrome disease model with induced pluripotent stem cells and differentiated cardiomyocytes. With the patient-specific cardiomyocytes, the disease phenotype of the autosomal recessive Noonan Syndrome was characterized comprehensively comprising genetic, cell biological, morphological, and functional characteristics. With pure, stable, and functional cultures of induced pluripotent stem cells and differentiated cardiomyocytes an autosomal recessive Noonan syndrome disease model was successfully established. Comprehensive analyses showed that the patient-specific cardiomyocytes recapitulate the hypertrophic phenotype in vitro and reveal disturbances in calcium handling, attenuated by verapamil treatment. Long-term treatment with verapamil could not influence the hypertrophic phenotype, considering this treatment as a symptomatic, non-causal treatment option. Additionally, a connection between leucine zipper like transcription regulator 1 loss-of- function and increased RAS-MAPK signaling activity was identified with transcriptome and proteome analysis. Protein expression alterations led to the generation of a specific protein signature of autosomal recessive Noonan syndrome with the potential to optimize the molecular classification and deciphering of pathogenesis. The reported human stem cell model of Noonan syndrome improves the current knowledge of the pathophysiological mechanisms, especially associated hypertrophic cardiomyopathy, and further serves as a platform for personalized medicine.
Keywords: Noonan Syndrome; iPSC; iPSC-CM; Disease Modeling; RASopathy; Stem Cells; RAS-MAPK pathway; LZTR1; Hypertrophic cardiomyopathy
 
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