POSTN and atrial fibrillation: COL1A1+ FibroNP is previously defined as adhesion/fibroNPC12 or C4 NPC.7 The FibroNP population was not reported in Wang et al scRNA-seq dataset, possibly because their cells were derived from the whole disc tissue without NP isolation and therefore may have dominated by COL1A1+ AF cells.11 Nonetheless, they defined the FibroNP genes (POSTN, COL1A1, COL3A1 and TMSB4X) in MK167+ progenitor and NP progenitor cells, implying the fibroblast presence within the two NP subtypes.