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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #57223
Title: IDENTIFICATION OF OSTEOCALCIN MRNA IN NONOSTEOID TISSUE OF RATS AND HUMANS BY REVERSE TRANSCRIPTION-POLYMERASE CHAIN REACTION

Author
item FLEET JAMES C - TUFTS-HNRCA
item HOCK JANET M - TUFTS DENTAL SCHOOL

Submitted to: Journal of Bone and Mineral Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: There is very little known about the continual process of bone formation and dissolution in the body, known as bone turnover. Osteocalcin, a protein released by osteoblasts or cells associated with bone turnover, attaches to bone tissue and is believed to be a marker for bone dissolution and reabsorption by the body. We studied the genetic messages, the link between genetic information and bodily function, of osteocalcin by modifying a method of measuring the genetic messages of certain proteins implicated in the formation of calcified tissues and bone. Although osteocalcin message levels are dramatically higher in bone, our results indicate that genetic messages for osteo- calcin are also present in tissues other than bone. We also showed that a vitamin D treatment in rats increased the level of genetic osteocalcin messages in bone but not in non-bone tissue. We have also detected low levels of osteocalcin messages in the aorta, the major artery leading from the heart. As a result of heart disease, when the vessel becomes clogged and frequently calcifies, the levels of the osteocalcin message were elevated suggesting that the diseased aorta takes on characteristics of bone. The relevance of our finding is unclear, but we believe further research is necessary to clarify the nature of osteocalcin and the osteoblasts and their relationship to the calcification of blood vessels.

Technical Abstract: Diseased or necrotic tissue can become calcified in a way that re- sembles bone. We examined soft tissues for the presence and regulation of the mRNA for the bone-associated protein, osteocalcin (OC). RNA was isolated from liver, kidney, lung, brain, muscle, and bone of young (2 months) male SD rats and analyzed for beta-actin, IGF-1, metallothionein IIa, alpha1 collagen, calbindin-D9k (CaBP), and OC mRNA by reverse transcription-polymerase chain reaction (RT-PCR), All PCR products but CaBP were found in bone; CaBP was present only in duodenum, kidney, and lung. OC product was detected in all tissues; the identity of the PCR product was confirmed by sequencing. Bone OC mRNA levels were calculated to be 1000-fold higher than duodenal levels. Rats fed a 0.8% strontium diet for 7 days to drive down serum 1,25-dihydroxyvitamin D3 levels (1, 25(OH)2D3) and then injected with 300 ng 1,25(OH)2D3/100 g body weight had increased duodenal CaBP(2.5-fold) and femur OC mRNA (2.2 fold) 24 h after treatment. Duodenal OC mRNA was unchanged. OC mRNA was found in nondiseased human aortae, and the amount of message was elevated in calcified aorta and calcified aortic plaques. These results demonstrate that (1) tissues other than bone have low basal expression of OC mRNA, (2) OC mRNA is not regulated by vitamin D in nonosteoid tissue, and (3) expression of OC mRNA in atherosclerotic aorta reflects a role for bone-forming cells in ectopic bone formation observed in certain disease conditions.