Novel enhancer activation non-restrictively followed a predefined framework in plastic vascular smooth muscle cells

Differentiated cells such as the plastic vascular smooth muscle cells (SMCs) could continue to develop after birth, mediated by continuously expanded enhancer network. However, it still remains unclear whether the adult enhancer network expansion follows a pre-designed path as seen during embryonic development, and how enhancers are selected for activation? Here, through systemic tracking of chromatin behaviors within vascular SMCs both in vivo and in vitro, we identified multiple collections of active enhancers exhibiting distinct behavioral patterns. Detailed epigenetic profiling further revealed these differentially behaved active enhancers were in distinct maturation states, characterized by varied sequential accumulation states for H3K4me1, H2A.Z and H3K27ac. H2A.Z was further found to recognize H3K4me1 and mediate initial H3K27ac modification that became stabilized later. This hit-and-stabilize process continued on new enhancer regions in vascular SMCs, but not in quiescent cardiomyocytes that also lacked H2A.Z accumulation. Further comparative study of human aortas at different ages also confirmed that new enhancer activation in adult non-restrictively followed a pre-designed path and reflected transformation history of vascular SMCs. Therefore, this newly clarified enhancer activation process would not only provide a new perspective for more accurately assessing the transformation history of aortic tissue, but also help to better understand the adult cell development in general.