Spatial Transcriptomics Uncovers Smooth Muscle Cell Loss And Tissue Disorganization In Thoracic Aortic Aneurysm With Bicuspid Aortic Valve

Background: Thoracic aortic aneurysm(TAA)is a potentially fatal disease caused by pathological dilatation of the thoracic aorta.It progresses slowly with no clear clinical signs in early stage,while in late stage it may cause aortic dissection or even rupture.Defects of vascular smooth muscle cell(SMC)are tightly related with TAA formation.Patients with the bicuspid aortic valve(BAV)are more likely to develop TAA than those with a normal tricuspid aortic valve(TAV),and the progression of TAA is more rapid.There is still no effective drug to prevent and treat TAA other than surgery,so there is an urgent requirement for a better understanding of the pathogenesis of TAA,especially in combination with BAV.Spatial transcriptomics,which preserves the spatial location of tissues and simultaneously resolves the transcriptomic information of tissues,is the latest generation of technology to study the transcriptome.There are no studies related to aortic aneurysms that have applied spatial transcriptomics yet.Objectives: Applying spatial transcriptome technology,we will reveal the spatial transcriptome characteristics of normal thoracic aorta,discover the spatial transcriptome changes in TAA,especially in BAVrelated TAA,uncover the pathogenesis of TAA,and explore potential therapeutic targets.Methods: A total of 63 patients were included in this study,and the final screening yielded spatial transcriptomic results in 17 patients,including 3 in the TAV Ctrl group,4 in the BAV Ctrl group,3 in the TAV TAA group and 7 in the BAV TAA group.We collected thoracic aortic tissues from patients in each group and validated the results derived from the spatial transcriptome using traditional molecular biology experimental techniques.We also cultured primary smooth muscle cells from the thoracic aortic tissues of patients in each group and used them to explore the signaling pathways associated with the pathogenesis of TAA.Results:1.The spatial transcriptome showed a total of three types of SMCs in normal thoracic aortic tissue and a clear hierarchical arrangement of these SMCs in space.2.The spatial transcriptome showed that the hierarchical arrangement of the different types of SMCs remained clear in TAV TAA,but the SMCs located in the inner media layer were lost in BAV TAA with abnormal valve function,resulting in a disrupted hierarchical arrangement.3.The expression of CCN3 and TGF-β signaling pathway-related proteins was increased in both TAV TAA and BAV TAA.In BAV TAA,GAS6 content was specifically reduced.4.Primary SMCs from BAV TAA have a higher propensity for apoptosis and have defects in proliferation and migration.Inhibition of the GAS6/AXL signaling pathway induced for a shift of TAV TAA primary SMC toward BAV TAA primary SMC,while activation of the GAS6/AXL signaling pathway promoted proliferation and attenuates apoptosis of BAV TAA primary SMC.Conclusion: This study applied the emerging spatial transcriptomics technology to reveal the unique spatial hierarchical arrangement of thoracic aortic tissues.It suggested disorder of SMC hierarchical arrangement caused by the loss of SMC in the media layer could be the pathogenesis of BAV TAA,and a new specific signaling pathways was identified associated with BAV TAA.This study establishes a novel theoretical basis for the formation of thoracic aortic aneurysms and provides new therapeutic ideas.