Bone Marrow–Derived ABCC6 Is an Essential Regulator of Ectopic Calcification In Pseudoxanthoma Elasticum

Abstract

Physiological calcification of soft tissues is a common occurrence in aging and various acquired and inherited disorders. ABCC6 mutations cause the calcification phenotype of pseudoxanthoma elasticum (PXE) as well as some cases of generalized arterial calcification of infancy (GACI), which is otherwise caused by defective ENPP1. ABCC6 is primarily expressed in liver, which has given the impression that the liver is central to the pathophysiology of PXE/GACI. The emergence of inflammation as a contributor to the calcification in PXE suggested that peripheral tissues play a larger role than expected. Here, we investigated whether bone marrow-derived ABCC6 contribute to the calcification in PXE. In Abcc6-/- mice we observed prevalent mineralization in several lymph nodes and surrounding connective tissues and an extensive network of lymphatic vessels within vibrissae, a calcified tissue in Abcc6-/- mice. Furthermore, we found evidence of lymphangiogenesis in PXE patients and mouse skin suggesting an inflammatory process. Finally, restoring wild type bone marrow in Abcc6-/- mice produced a significant reduction of calcification suggesting that the liver alone is not sufficient to fully inhibit mineralization. With evidence that ABCC6 is expressed in lymphocytes, we suggest that the adaptative immune system and inflammation are significant contributors to the calcification in PXE/GACI.