SPATIAL TRANSCRIPTOMICS REVEAL GENE EXPRESSION SIGNATURE IN ARTERIAL FIBROMUSCULAR DYSPLASIA LESIONS

Objective: Fibromuscular dysplasia (FMD) is a group of arterial lesions, mainly successive stenosis and aneurysms, which present in the context of hypertension, stroke and myocardial infarction due to spontaneous coronary artery dissection (SCAD). Our recent genetic studies showed FMD to share many risk genes with these diseases, mainly with SCAD, where ∼50% of patients present extra-coronary FMD-type arteriopathies. We aimed to explore gene expression signatures to yield insights into FMD specific arterial remodeling. Design and method: We identified 11 FMD and 9 non-FMD arterial formalin-fixed paraffin-embedded tissue samples. We selected 6 FMD and 2 non-FMD samples for 10x Visium spatial transcriptomic sequencing (Illumina NextSeqTM 500) based on immunostaining results and high RNA quality. Raw fastq files corresponding to CytAssist images were processed using Space Ranger’s pipeline ‘count’ (10x Genomics Space Ranger v3.0.0). Differential expression analyses between cell clusters and samples were conducted using Seurat (v5.0.3) in R (v4.3.3). Cell types were inferred using public single-cell reference datasets of human arteries. Enrichment analyses were conducted using clusterProfiler (v4.10.1). Results: We analyzed six samples (4 FMD, 2 non-FMD) after quality control filtering with an average of 2,787 spots per sample and mapping rates > 97%. Clustering based on gene expression identified 10 groups, with three (M1–M3) were located in the media and seven (A1–A7) in the adventitia, with intima layer virtually uncaptured due to the lack of resolution. Cell type inference showed that M1, M2, and M3 clusters primarily consisted of smooth muscle cells (SMCs), with marker genes MYH11 and TAGLN highly expressed. M3 uniquely exhibited high expression of several collagen genes, and was predominantly found in FMD lesions (7.5% vs. 0.3% in non-FMD). Pathway analyses revealed upregulation of several genes linked to extracellular matrix (ECM) biology in FMD lesions while genes related to contractile fibers were downregulated. Conclusions: Our data suggest increased fibrosis markers and loss of contractile SMC function in FMD lesions, compared to non-FMD arterial tissues. Our current efforts aim to validate these findings using histology to follow up some candidate gene expression signatures of tissue remodeling and SMC function in FMD lesions.