THE ROLE OF DERMAL FIBROBLASTS IN THE DEVELOPMENT OF ECTOPIC CALCIFICATIONS

Soft connective tissues calcifications (i.e. ectopic calcifications) represent a deleterious consequence of diabetes, renal disorders and aging, being a key determinant of cardiovascular morbidity and mortality. Although the molecular pathways leading to this undesired mineralization have been largely investigated in smooth muscle cell cultures (SMC), to date no effective treatments are available. In order to further investigate the process of ectopic calcifications, an in vitro calcification assay has been established by isolating dermal fibroblasts (DF) from healthy adult individuals and from patients affected by Pseudoxanthoma elasticum, a disease characterized by progressive calcification of elastic fibres. Cells were grown up to 30 days in standard or in a calcifying medium. The degree of mineralization was evaluated after Von Kossa staining, whereas markers of calcification (ALP, ANKH, BMP2, ENPP1, MGP, SPP1) were assessed by RT-PCR and Western Blot. Results demonstrate that: 1) in contrast to SMC, DF do not develop a calcifying signature, 2) changes in the expression of some osteogenic markers are more related to the aging of cell cultures, 3) the development of a calcified matrix is tightly dependent on the characteristics of the extracellular environment, 4) increased ALP activity is necessary but not sufficient to have mineral deposit formation; 5) the complex balance between pro- and anti-calcifying factors, including circulating factors as MGP and fetuin, plays a significant role in the occurrence of ectopic calcifications in vivo.