MEASUREMENT OF MESSENGER-RNA LEVELS IN THE PERIOSTEUM OF AGING RATS

This report describes a new in vivo rat model to study regulation of mRNA levels in skeletal tissues. The periosteum from the tibial diaphysis of adult male rats was harvested after collagenase treatment. Northern analysis of total RNA isolated from periosteum revealed that periosteal bone cells expressed genes for osteoblast markers, including the bone matrix proteins osteocalcin (BGP), pre-pro-alpha 2(I) chain of type 1 precollagen (collagen), osteopontin (OP), and osteonectin (ON), the osteoblast marker enzyme alkaline phosphatase (AP), and the osteoblast- derived signaling factor transforming growth factor beta (TGF-beta). Mature rats (12 month) had lower steady-state mRNA levels for collagen and BGP than did young adult (4 month-old) rats. The periosteal bone formation rate was determined in the same specimens used to assay mRNA levels and was found to bc decreased in the older rats. The results of these studies suggest that the number of mRNA transcripts for bone matrix proteins decrease in periosteum during aging and that this change accompanies and may mediate a corresponding decrease in bone formation.