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 hum ans and animals. Although intact human PTH has 84 amino acids, the N-termin al 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 d ose-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 fe mur metaphyses. We selected AP-1 genes, which include jun and fos, as they play a fundamental role mediating signals for proliferation, differentiatio n, and apoptosis in cells of different origins, including bone, and are kno wn 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 dos e; 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. Expr ession 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 aft er 1, 3, or 7 days of once-daily subcutaneous treatment of either peptide. When individual comparisons for each dose between peptides were made, the m inimum effective dose necessary to stimulate a significant increase in c-fo s and junB expression was equivalent for both peptides. The minimum effecti ve dose for hPTH(1-34) was at least tenfold lower than hPTH(1-84) in stimul ating 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-dai ly 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 dat a on molecular regulation in mouse bone confirm and extend prior data from rat studies showing equivalence on bone mass at equimolar doses. (C) 2000 b y Elsevier Science Inc. All rights reserved.