Matrix Pathobiology Elastin Calcification in the Rat Subdermal Model Is Accompanied by Up-Regulation of Degradative and Osteogenic Cellular Responses

Calcification of vascular elastin occurs in patients with arteriosclerosis, renal failure, diabetes, and vascular graft implants. We hypothesized that pathological elastin calcification is related to degenerative and osteogenic mechanisms. To test this hypothesis, the temporal expression of genes and proteins associated with elastin degradation and osteogenesis was examined in the rat subdermal calcification model by quantitative real-time reverse transcription-polymerase chain reaction and specific protein assays. Purified elastin implanted subdermally in juvenile rats exhibited progressive calcification in a time-dependent manner along with fibroblast and macrophage infiltration. Reverse transcription-polymerase chain reaction analysis showed that relative gene expression levels of matrix metalloproteinases (MMP-2 and MMP-9) and transforming growth factor1 were increased in parallel with calcification. Gelatin zymography showed strong MMP activities at early time points, which were associated with high levels of soluble elastin peptides. Gene expression of core binding factor -1, an osteoblast-specific transcription factor, increased in parallel with elastin calcification and attained 9.5-fold higher expression at 21 days compared to 3 days after implantation. Similarly, mRNA levels of the bone markers osteopontin and alkaline phosphatase also increased progressively, but osteocalcin levels remained unchanged. We conclude that degenerative and osteogenic processes may be involved in elastin calcification. (Am J Pathol 2006, 168:490–498; DOI: 10.2353/ajpath.2006.050338)