DDR2 and hydrops fetalis: Like primary HSCs, both cell lines express key receptors regulating HF, including platelet-derived growth factor receptor β (βPDGF-R), obese receptor long form (Ob-RL), and discoidin domain receptor 2 (DDR2), and proteins involved in matrix remodeling, such as MMP-2, TIMP-2, and membrane-type I matrix metalloproteinase (MT1-MMP).