The role of m6A RNA Modifications in Vascular Smooth Muscle Cell Plasticity

Vascular smooth muscle cells (VSMCs) display extraordinary phenotypic plasticity. This allows them to differentiate or dedifferentiate, depending on environmental cues. The ability to ‘switch’ between a quiescent contractile phenotype to a highly proliferative synthetic state renders VSMCs as primary mediators of vascular repair and remodelling. When their plasticity is pathological, it can lead to cardiovascular diseases such as atherosclerosis and restenosis. The role of the N6-methyladenosine (m6A) RNA modification in VSMC plasticity is as yet unknown. m6A is the most prevalent chemical modification on messenger RNA and is a highly conserved phenomenon which facilitates altered gene expression control. The aim of this research was to determine how m6A and its regulatory factors are altered in VSMC plasticity, and how these changes impact VSMC gene expression. Using robust primary murine VSMC models in vitro, and arterial injury models in vivo, this study indicated that Mettl14, an essential component of the m6A-depositing machinery, may be an important promoter of VSMC dedifferentiation. Profiling of m6A in Mettl14-deficient VSMCs revealed that essential VSMC gene networks and functional pathways are subject to altered m6A regulation. Furthermore, in-depth study of key m6A-affected VSMC transcripts, including Serpine1, Lpar2 and Klf4 showed that Mettl14 enhances their expression via increased m6A deposition. For Serpine1, this was also found to be strongly reflected at the protein level. The stability of these transcripts was not greatly altered in Mettl14-deficient cells, indicating that their differential expression may be due to co-transcriptional regulation instead. These findings contribute to the growing evidence that m6A is an essential phenomenon in a range of cellular processes, and provides novel insight into the molecular underpinnings of VSMC plasticity