Dolph Houben

105 Neoangiogenensis, transplant viability and molecular analysis of bone VCA 5 Gene expression analyses Bone homeostasis and remodeling markers To examine the biological effect of vascularized allotransplantation on the bone homeostasis, we compared the expression of important osteoblast and osteoclast genes in normal bone and in our allotransplant groups. The Tumor Necrosis Factor superfamily of ligands ( TNFSF11/ osteoclast marker) and receptors ( TNFRSF11B/ osteoblast marker) provide key paracrine communication signals for the differentiation of osteoclasts [15] . These genes are also known as Receptor Activator of Nuclear factor Kappa-B Ligand and Osteoprotegerin ( RANKL/OPG ) [16] . This interplay mirrors the important role of osteoblasts on osteoclast differentiation [17] . Cathepsin K ( CTSK ), which encodes a lysosomal cysteine protease involved in bone remodeling and resorption, is predominantly expressed by osteoclasts. Bone Gamma-Carboxyglutamate Protein ( BGLAP ), also known as osteocalcin, is a protein secreted by osteoblasts that regulates bone remodeling and energy metabolism [15] . Although we did find numerical differences between the groups, differences in important osteoclast ( CTSK ) and osteoblast ( BGLAP ) markers were not statistically significant. There were neither statistically significant nor biologically-relevant differences in biomarkers for bone homeostasis ( RANKL, OPG ) and bone remodeling ( CTSK, BGLAP ) between the groups or compared to normal bone. Thus, bone homeostasis and remodeling appear to be comparable between treatment groups as measured by gene expression analyses (Fig. 4).