ALK-3

ALK-3 is the receptor bone morphogenetic protein (BMP) type I receptors, for BMP2, BMP4, GDF5 and GDF6. Among BMP type I receptors, ALK-2 and 3 are widely expressed in tissues, while ALK-1 is more selectively expressed in endothelial cells (ECs)^[1]. Hepcidin, the main regulator of iron metabolism, is synthesized and released by hepatocytes in response to increased body iron concentration and inflammation. BMP/ALK/SMAD pathway controls hepcidin expression, while BMP type I receptors ALK-2 and ALK-3 are responsible for iron-dependent hepcidin upregulation and basal hepcidin expression, respectively, to avoid low hepcidin which causes iron overload or high hepcidin levels which induce iron-restricted erythropoiesis^[2]. ALK-3 positively regulates chondrocyte differentiation through GDF5 interaction and mediates induction of adipogenesis by GDF6^[3]. ALK-3 protein shows function for the initiation of chondrogenesis, for regulating differentiation along the chondrogenic lineage, and for endochondral bone formation^[4]. Components of BMP signaling have been implicated in both pathogenesis of pulmonary arterial hypertension (PAH) and endothelial-mesenchymal transition (EndoMT), and BMPR1A is key to maintain endothelial identity and to prevent excessive EndoMT. BMPR1A-ID2/ZEB1-TGFBR2 signaling axis could serve as a potential novel target for PAH and other EndoMT-related vascular disorders^[5].