Spatial gene expression of human coronary arteries revealed the molecular features of diffuse intimal thickening in explanted hearts
Authors: Li Boaz , Leung Samuel , Elishaev Maria , Cheng Wan Hei , Mocci Giuseppe , Björkegren Johan L.M. , Lai Chi , Singh Amrit , Wang Ying 
Published: January 2025

Background

Diffuse intimal thickening (DIT) is a pre-clinical stage of atherosclerosis characterized by thickened intima. The molecular basis of its susceptibility to atherogenesis is unknown, and mechanistic investigations cannot be performed in commonly used mouse models, in which DIT does not exist. Vascular smooth muscle cells (SMCs) are the predominant cell type that occupies the intima and media of DIT. The molecular differences between these two layers may reveal the earliest phenotypic changes in SMCs to promote atherosclerosis.

Methods

We benchmarked the RNA quality of human coronary arteries from autopsies (n=7) and freshly explanted hearts (n=7) and performed Visium spatial gene expression on tissue sections with DIT. SMC-enriched intima and media were compared to find differentially expressed genes. The gene ontology features of SMC-enriched intima in this study were also compared to those in the atherosclerotic lesions, as previously revealed by single-cell RNA-sequencing studies.

Results

Although autopsy samples met the RNA quality standard for Visium (DV200 ≥ 30%), only arteries from freshly explanted hearts exhibited reliable performance. Genes enriched in TGF-β-mediated remodeling of the extracellular matrix were overrepresented in the intima, including versican and biglycan. SMCs enriched in the intima are dedifferentiated, but unlike those in the lesions, they are not proinflammatory.

Conclusions

Our findings indicate that autopsy samples are not ideal to distinguish subtle differences among cell phenotypes. Dedifferentiated SMCs in the DIT are distinct from the proinflammatory SMCs in atherosclerotic lesions. SMCs in thickened intima may lead to lipid retention but not necessarily the onset of atherosclerosis.

Research Perspective:

1) What is New?

Postmortem coronary arteries, which are frequently collected by biobanks, have degraded RNA, which are not suitable for identifying subtle differences in the transcriptome profiles.

Coronary arteries from explanted hearts allow for more faithful representation of spatial gene expression across the vessel wall as compared to ones from autopsy hearts.

Thickened intima in diffuse intimal thickening, which exists in everyone, is unlikely to undergo atherogenesis without additional stimuli such as inflammation.

2) What Question Should be Addressed Next?

The current RNA quality standard of spatial transcriptomics needs to be carefully benchmarked in biobank samples to control sequencing performance and meaningful data interpretation.

How inflammation changes smooth muscle cell phenotypes may explain why everyone has diffuse intimal thickening, but those with chronic inflammatory disease have a high risk of coronary artery disease.

Future research should focus on the interplay between smooth muscle cell phenotypes and the extracellular matrix to understand the etiology of coronary artery disease.