Higher Expression of Collagen-binding Small Leucine-rich Proteoglycan Genes in Mouse Mandibular Bone Marrow than Femoral Bone Marrow

Abstract

Although the craniofacial and the appendicular bones develop embryologically from different origins and show different architectures and functions, it is still unclear if there exist site-specific genetic and phenotypic differences in these bones. The aim of this study was to analyze the gene expression levels of collagen-binding small leucine-rich proteoglycans (SLRPs) and type I collagen (COLI), the major matrix proteins in bone, in mouse mandibular and femoral bone marrows. Histomorphometrical and real-time PCR analyses were performed on the two bones of two senescence-accelerated mouse (SAM) strains. SAMP8 and SAMR1, with potentially different bone phenotypes. In both mice, the trabecular bone volume was 10 times higher at the mandibular neck than at the femoral distal metaphysis. The volume in the femur but not in the mandible was slightly higher in SAMR1 than in SAMP8. The mRNAs of COLI and collagen-binding SLRPs, except decorin, were higher in the mandibular bone marrow than in the femoral marrow. Although the femoral marrow did not express fibromodulin and lumican in both mouse strains and biglycan in the SAMR1 strain, they were highly expressed in the mandibular marrow. High gene expression of these molecules in the mandibular bone may imply active bone formation and remodeling in this bone tissue.