Lineage-Specific Phenotypic Abnormalities in iPSC-Derived Smooth Muscle Cells from Type-I Loeys-Dietz Syndrome

Loeys-Dietz syndrome (LDS) is a connective tissue disorder caused by mutations in genes encoding components of the transforming growth factor (TGF)-β pathway. This condition increases the risk of developing a potentially fatal thoracic aortic aneurysm (TAA) and dissection, yet the mechanisms underlying TAA development remain unclear. In LDS, TAAs frequently develop at the aortic root, where smooth muscle cells (SMCs) from two distinct embryonic origins – the lateral mesoderm (LM) and neural crest (NC) – are intermingled. SMCs are hypothesised to be the key cell type contributing to TAA development. However, only LM-SMCs showed abnormal functionalities in LDS, while NC-SMCs remained unaffected. We hypothesised that this discrepancy arises from lineage-specific differences in the regulation of the TGF-β signalling pathway. To investigate this pathway, we used patient-derived induced pluripotent stem cells (iPSCs) carrying a heterozygous TGFBR1+/R487Q mutation and its mutation-corrected isogenic control iPSCs to model Type-I LDS. Phenotypic characterisation, such as by bulk RNA sequencing, revealed that LM-SMCs have abnormal phenotypes, including impaired TGF-β signalling, irregular expression of extracellular matrix, contractility defect, inability to regulate cell proliferation, poor cellular motility, and mitochondrial abnormality. In contrast, these defects were not detected in NC-SMC. Quantitative proteomics identified a significantly higher TGFBR1 protein level in NC-SMCs compared to LM-SMCs, potentially compensating for a reduced copy number of WT TGFBR1 and protecting NC-SMCs against the detrimental effects of the mutation. Additionally, ubiquitin-conjugating enzyme E2 L3 (UBE2L3), a regulator of TGFBR1 degradation, was upregulated in LM-SMCs relative to NC-SMCs. Silencing UBE2L3 expression in LM-SMCs did not restore TGF-β signalling and mitochondrial functions, but modestly improved contractility, though the effect was not statistically significant. In conclusion, our study demonstrates that TGFBR1+/R487Q mutation differentially impacts LM-SMCs and NC-SMCs, potentially due to lineage-specific differences in TGFBR1 protein levels. These findings suggest that modulating TGF-β signalling in LM-SMCs to mimic NC-SMCs may offer new therapeutic opportunities against TAA development in LDS.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Lo, Yuanxi Motohiro Franklin

Advisor dc:contributor.advisor

• Sinha, Sanjay

• smooth muscle cell
• Loeys-Dietz syndrome
• Aortic aneurysm

Licence

• https://www.repository.cam.ac.uk/bitstreams/dd90d187-81a5-4ce7-b74e-e9648c78f99a/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.120885

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/388622