In vivo comparison of activated protein-1 gene activation in response to human parathyroid hormone (hPTH)(1-34) and hPTH(1-84) in the distal femur metaphyses of young mice.
Intermittent parathyroid hormone (PTH) treatment increases bone mass in humans and animals. Although intact human PTH has 84 amino acids, the N-terminal 31 to 38 amino acids are sufficient for bone anabolic activity in vivo. Prior studies have evaluated hPTH(1-34) and hPTH(1-84) with respect to bone mass increase and quality, but there have been no in vivo comparisons of dose-dependent molecular responses. After confirming that young male BALB/c mice respond to daily PTH with increased bone mass, we profiled the steady-state mRNA levels of activating protein-1 (AP-1) genes regulated by hPTH(1-34) and hPTH(1-84) at doses ranging from 0 to 19.4 nmol/kg in the distal femur metaphyses. We selected AP-1 genes, which include jun and fos, as they play a fundamental role mediating signals for proliferation, differentiation, and apoptosis in cells of different origins, including bone, and are known to be regulated by PTH. Human PTH(1-34) and hPTH(1-84) increased steady-state mRNA expression of c-jun, junB, c-fos, and fra-2 in an equivalent dose- and time-dependent manner. Expression of fosB or fra-1 was not detected with either peptide. When averaged across dose and time, responses to hPTH(1-34) and hPTH(1-84) were not significantly different from each other. Expression of c-jun, junB, and c-fos peaked 30 minutes after the injection while fra-2 expression peaked 30 minutes later. All AP-1 genes stimulated by PTH returned to the levels of vehicle treated controls by 3 h after injection. The expression level of junD, which was abundant in the distal metaphysis, was not altered by either peptide. No change in magnitude was observed after 1, 3, or 7 days of once-daily subcutaneous treatment of either peptide. When individual comparisons for each dose between peptides were made, the minimum effective dose necessary to stimulate a significant increase in c-fos and junB expression was equivalent for both peptides. The minimum effective dose for hPTH(1-34) was at least tenfold lower than hPTH(1-84) in stimulating c-jun and fra-2 expression. Area under the curve for the highest dose (19.4 nmol/kg) of either peptide showed no significant differences in the expression of any of the genes. In conclusion, in young mice given once-daily subcutaneous injections up to 7 days, hPTH(1-34) and hPTH(1-84) induced equivalent responses by time and dose in the selected AP-1 genes. These data on molecular regulation in mouse bone confirm and extend prior data from rat studies showing equivalence on bone mass at equimolar doses.
Stanislaus
D
D
Lilly Research Laboratories, Indianapolis, IN 46202, USA.
Devanarayan
V
V
Hock
J M
JM
D000367:Age Factors; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005269:Femur / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D016762:Genes, fos / Q000502:physiology; D016758:Genes, jun / Q000502:physiology; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009929:Organ Size; D010006:Osteoblasts / Q000187:drug effects / Q000502:physiology; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000235:genetics*; D000099169:Fos-Related Antigen 1
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D000099169:Fos-Related Antigen 1