CD44 and atrial fibrillation: Other cell populations have also been described more recently in the AF, such as: innate progenitor cells identified by immunolocalization of CD24, CD44, CD29 or CD105 (Daly et al. 2016; Chan et al. 2014; Choi et al. 2015) with additional stem cell markers like platelet-derived growth factors or CD90 (Daly et al. 2016; Stein et al. 2021) and (MSC)-like cells, also seen in NP verified through osteogenesis, chondrogenesis, and adipogenesis assays (Tang et al. 2012).