title: Decline in calcitonin receptor expression in osteocytes with age.
abstract: We have previously shown that co-administration of the transient osteoclast inhibitor, salmon calcitonin (sCT), blunts the anabolic effect of parathyroid hormone (PTH) in young rats and increases osteocytic expression of the bone formation inhibitor sclerostin (Sost). To determine whether this also occurs in adult animals, we co-administered sCT with PTH to 6-month-old sham-operated (SHAM) and ovariectomised (OVX) rats. While sCT reduced the stimulatory effect of PTH on serum amino-terminal propeptide of type 1 procollagen levels, in contrast to its influence in young rats, sCT did not reduce the anabolic effect of PTH on femoral bone mineral density, tibial trabecular bone volume or bone formation rate in 6-month-old SHAM or OVX rats. Quantitative real-time PCR analysis of femoral metaphyses collected 1 and 4 h after a single PTH injection confirmed a significant increase in mRNA levels for interleukin 6 (Il6) and ephrinB2 (EfnB2), and a significant reduction in Sost and dentin matrix protein-1 (Dmp1) in response to PTH. However, in contrast to observations in young rats, these effects were not modified by co-administration of sCT, nor did sCT significantly modify Sost, Dmp1, or matrix extracellular phosphoglycoprotein (Mepe) mRNA levels. Furthermore, while CT receptor (CTR) mRNA (Calcr) was readily detected in GFP+ osteocytes isolated from young (3-week-old) DMP1-GFP mice, Calcr levels in osteocytes declined as mice aged, reaching levels that were undetectable in long bone at 49 weeks of age. These data indicate that osteocyte-mediated responses to CT are most likely to be of physiological relevance in young rodents.
authors: St Vincent's Institute, and Department of Medicine, at St Vincent's Hospital, The University of Melbourne, 9 Princes Street, Fitzroy, Victoria 3065, Australia Nordic Bioscience Inc., Copenhagen, Denmark.
authors: Jonathan H
authors: JH
authors: Gooi
authors: Ling Yeong
authors: LY
authors: Chia
authors: Nicole C
authors: NC
authors: Walsh
authors: Morten A
authors: MA
authors: Karsdal
authors: Julian M W
authors: JM
authors: Quinn
authors: T John
authors: TJ
authors: Martin
authors: Natalie A
authors: NA
authors: Sims
mesh_terms: D000375:Aging / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002116:Calcitonin / Q000494:pharmacology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D051379:Mice; D008822:Mice, Transgenic; D010011:Osteocytes / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018003:Receptors, Calcitonin / Q000235:genetics* / Q000378:metabolism
chemical_list: D018003:Receptors, Calcitonin; C028815:salmon calcitonin; D002116:Calcitonin
keywords: PTH; calcitonin; coupling; osteoclast; osteocyte; sclerostin