Abstract P470: Disrupted HRAS/GRB2 Signaling In Induced-cardiomyocytes Derived From Patients With Noonan Syndrome Carrying SOS1 Gene Mutation

Background: Noonan syndrome (NS), a dominant autosomal genetic disorder that prevents normal development, and exhibits cardiac defects, which is estimated to appear in 50% to 90% of patients. Son of sevenless homolog 1 (SOS1) gene mutation has been identified as a major gene causing NS and attributes to the development of cardiomyopathy and congenital heart defects. SOS1 is a guanine nucleotide exchange factor for RAS and is known to interact with growth factor receptor-bound protein 2 (GRB2). Recently, we have generated induced pluripotent stem cells (iPSCs)-derived cardiomyocytes (iCMCs) from cardiac fibroblasts obtained from a NS patient carrying SOS1 gene variant 1654A>G. Hypothesis: Since NS is known to have aberrant RAS-MAPK signaling, we hypothesize that iCMCs derived from NS patient (NS-iCMCs) may have atypical RAS signaling leading to the development of cardiomyopathy. Methods and Results: We have compared the normal skin fibroblast-derived iPSCs (N-iPSCs) and N-iCMCs with NS patient-derived induced NS-iPSCs and NS-iCMCs. Our qRT-PCR results showed that the mRNA expressions of signaling molecules HRAS, GRB2 and SOS1 were significantly decreased in NS-iCMCs compared with N-iCMCs (Figure A), and further confirmed through the protein expression by Western immunoblotting (Figure B). These results were in association with a significantly decreased mRNA and protein expressions of cardiac transcription factor GATA4, and structural proteins alpha sarcomeric actinin-2 (ACTN2), cardiac troponin T (TNNT2) and tropomyosin alpha-1 (TPM1) in NS-iCMCs compared with N-iCMCs. Further studies are underway to explore the difference in the guanine nucleotide exchange factor (GEF) activity and ERK activation between NS-iCMCs and N-iCMCs. Conclusion: Our current findings clearly indicate that the SOS1-associated signaling molecules HRAS and GRB2 were disrupted in NS-iCMCs, which may result in the development of cardiomyopathy in NS patients.