Introduction Vascular smooth muscle cells (VSMCs) show inherent plasticity, enabling their phenotypic switch into a synthetic state for vascular repair and remodelling. Under inflammatory conditions, this contributes to atherosclerotic plaque development, with VSMCs demonstrated to produce multiple plaque-resident cell types. However, only a small fraction of VSMCs participate in disease associated proliferation1 and it is unclear if this is a defined subset within the heterogeneous population.
Methods Here we performed transcriptional profiling of dissociated VSMCs from two discrete aortic regions; the plaque-susceptible aortic arch (AA) and resistant descending thoracic aorta (DT). Differentially expressed genes were identified using both conventional and single cell RNA sequencing. This differential expression was then validated by RT-qPCR and single molecule RNA fluorescence in situ hybridisation (smRNA-FISH), implemented to interrogate candidate gene expression at a single-cell level.
Results RNA sequencing analysis demonstrated differential expression of 227 genes between the AA and DT regions, with consistency in the profiling data from conventional and single cell sequencing. These results correlate with earlier work to profile these regions; for example, we found upregulation of homeobox genes in the DT relative to the AA, which has been previously observed2. However, many of the genes identified are distinct from those previously characterised and our single cell analysis demonstrated heterogeneity between individual cells within the same region. In particular, certain genes were highly expressed in only a subset of AA cells, including Pde1c, an enzyme shown to promote VSMC proliferation3. Patterns in expression were validated for candidate genes, selected by VSMC or disease relevance. This showed similar fold changes in expression between the two regions by RT-qPCR and RNA sequencing, with ongoing smRNA-FISH investigations into their cell to cell variation.
Conclusions Our characterisation of VSMC expression patterns showed both regional and local heterogeneity and suggested the presence of a subset of AA cells with a unique expression profile. These cells might be those responsible for the clonal proliferation we observed in disease1, which would explain the AAs heightened plaque susceptibility. Our identified differentially expressed candidate genes may mark or regulate this population, aiding future investigations into the mechanisms underlying plaque development.
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